The primary entry point is the Helpdesk. Add a new section (link "New section") to that page and ask the question on how to do something (or asking for a reference to how to do something).
Unfortunately the original URL to a Helpdesk entry becomes broken when it rolls off the main page and onto an archive page. The way to find the new URL is first to note down the date of the question (for example, use "My contributions" - top right on a page when logged in) and then locate the entry on a Helpdesk archive page.
A quantity and unit should be separated by space! From MOS:UNITS, Unit symbols: "Values and unit symbols are separated by a non-breaking space. The {{nowrap}} template or the character can be used for this purpose. For example, use 10 m or 29 kg, not 10m or 29kg."
When values and spelled-out units form a compound adjective, hyphenate them: 10-kilometer beach, but 10 km beach. From Tony1's manual of style. This is also stated in MOS:UNIT, Unit names.
Low numbers: first or one, second or two, third or three, etc. (not 1st or 1, 2nd or 2, 3rd or 3, etc.). From WP:ORDINAL: "single-digit whole numbers from zero to nine are spelled out in words".
Contractions. it's, don't, didn't, won't, etc. should be expanded to it is, do not, did not, will not, etc. Ref: style manual, Contractions. See also Basic copyediting, Common edits, "Unless part of a quotation, contractions (don't, can't, etc.) should be changed to non-contracted forms (do not, cannot, etc.).".
Line-break protection. To protect from line-break for things with non-spaces use the nowrap template (can also be used with space as an alternative to ). Examples: {{nowrap|A/D}} and {{nowrap|Mac OS X}}. Note that this template does not appear to work well with links, but this works (put the link inside the template): {{nowrap|[[Mac OS X]]}}
Numbers
Template for listing two types of units with one source, "convert". Example with a limit of 2 significant figures: {{convert|50000|kg|lb|lk=on|sigfig=2}}. Result: 50,000 kilograms (110,000 lb). "lk=on" makes wiki links to both input and output unit; normally it should be left out, equivalent to "lk=off".
Use "abbr=on" for the short form (e.g. m² instead of square metres).
If the quantity of the output unit (in the parentheses) is known then use "disp=flip". Example: {{convert|35|oz|kg|disp=flip|sigfig=2|abbr=on}}. Output: 0.99 kg (35 oz).
"The initial letter of a title is capitalized ... used only where they would be used in a normal sentence ... (Funding of UNESCO projects, not Funding of UNESCO Projects)."
"use "and" instead of an ampersand (&)"
Bulleted and numbered lists - "When the elements are complete sentences, they are formatted using sentence case and a final period."
Layout. "This Wikipedia Guide to Layout is a guide to laying out a typical basic article."
Conform to style guide, copy editing: {{Cleanup}}.
"This article is written like an advertisement.": {{Advert|date=January 2013}}.
When an article uses external links in the body (for instance, instead of references): {{Citation style|date=January 2013|details=Violates Wikipedia:External links: "Wikipedia articles may include links to web pages outside Wikipedia (external links), but they should not normally be used in the body of an article."}}. (Wikipedia:External links says: "Wikipedia articles may include links to web pages outside Wikipedia (external links), but they should not normally be used in the body of an article."). Helpdesk entry. There is also the template external links, {{External links|date=January 2013}}. Output: "This article's use of external links may not follow Wikipedia's policies or guidelines. Please improve this article by removing excessive and inappropriate external links. (January 2013)"
Keyboard formatting (three keys in this example): {{keypress|Left CTRL|Left SHIFT|Left ALT}}. In action: Left CTRL+Left SHIFT+Left ALT
Do not use the second person (you, your). From Second-person pronouns (MOS:YOU): "Use the third person (a noun, or he, one, etc.): instead of When you move past "Go", you collect $200, use When players pass "Go", they collect $200, or A player passing "Go" collects $200. The passive voice may sometimes be used instead: When "Go" is passed, $200 is collected."
No "'" in decade designations; instead of 1930's, 1940's, 1950's, 1960's, it should be 1930s, 1940s, 1950s, 1960s. Ref: WP:DECADE, "Decades".
No "&" (ampersand) in normal text. Replace "&" with "and". Ref: MOS:AMP.
Regular expressions (Perl type) for matching missing space between quantity and unit ("\[*" is for handling wikified units and "'*" is for italicised units). Also note that there are normally a lot of false positives and thus every match must be checked manually. Also, there are some internal false positives (that can be fixed, though, by changing the regular expression), e.g. "10 V/cm" will currently match. The symbol for micro can have several representations, e.g. 0xB5 and 0x55 0xCE 0xBC - they usually look slightly different: µμ.
\d'*\[*-*[kKmMgGtT]i*[bB] Bits and bytes. Example of incorrect: 8GB
\d'*\[*-*[kKmMgG]*[hH]z Frequency. Examples of incorrect: 17.8kHz, 900MHz
\d'*\[*-*[gGkKmMµμnNpP]*[vVwWaA] Electricity. Examples of incorrect: 220V, 67.1volts
\d'*\[*-*[mMuUµμnNpP]*[fFhHΩ] Electronic components. Examples of incorrect: 100nF, 7.5µH, 49.9Ω.
\d'*\[*-*[mMµμnNpP]*[sS] Time. Examples of incorrect: 110ms, 67.87ps, 30seconds
\d'*\[*-*[cCkKmMµμnN]*[mM] Physical dimensions. Examples of incorrect: 10km, 45.3nm
\d'*\[*-*[ifl][ntb] Imperial units. Examples of incorrect: 65in, 78.1lb
\d'*\[*-*[kmMµμnNpP]*[g] Mass. Examples of incorrect: 4,500kg, 89.2µg
\d'*\[*-*[mµμnNpP]*[lL] Volume. Examples of incorrect: 12.8l, 89nl
\d'*\[*-*[°][CF] Temperature. Examples of incorrect: 50°C
\d'*\[*-*[N] Force. Examples of incorrect: 0.15N
\d'*\[*-*dB*[muv]* Ratios 1 (for example power or intensity). Examples of incorrect: 78dB, -45.2dBm
\d'*\[*-*pp[mb] Ratios 2. Examples of incorrect: 2.5ppm, 68ppb.
\d'*\[*-*[kilowatt] Particular units, 1. Examples of incorrect: 7.5kilowatts
\d'*\[*-*[picofarad] Particular units, 2. Examples of incorrect: 100picofarad
Other
\d[aApP]\.*[mM] Time of day. Examples of incorrect: 7AM, 9:30pm
\d\s+[AP][M]|\d\s+[ap][m] Time of day. Examples of incorrect: 7AM, 9:30pm (?)
\d\[*-*[mMkKgG]*[lL][yY]|\d\[*-*[mMkKgG]*[pP][cC]|\d\[*-*[aA][uU] Astronomical, e.g. distance i parsecs (pc) or light years (ly). Examples of incorrect: 360kpc, 145Mly, 85AU.
All combined: \d'*\[*-*[kKmMgGtT]i*[bB]|\d'*\[*-*[kKmMgG]*[hH]z|\d'*\[*-*[gGkKmMµμnNpP]*[vVwWaA]|\d'*\[*-*[mMuUµμnNpP]*[fFhHΩ]|\d'*\[*-*[mMµμnNpP]*[sS]|\d'*\[*-*[cCkKmMµμnN]*[mM]|\d'*\[*-*[ifl][ntb]|\d'*\[*-*[kmMµμnNpP]*[g]|\d'*\[*-*[mµμnNpP]*[lL]|\d'*\[*-*[°][CF]|\d'*\[*-*[N]|\d'*\[*-*dB*[muv]*|\d'*\[*-*pp[mb]|\d[aApP]\.*[mM]|\d\s+[AP][M]|\d\s+[ap][m]|\d'*\[*-*[kilowatt]|\d\[*-*[mMkKgG]*[lL][yY]|\d\[*-*[mMkKgG]*[pP][cC]|\d\[*-*[aA][uU]
Ideas for the future:
Do some prefiltering before the matching, e.g. to remove reference sections (<ref></ref>). This should significantly reduce the number of false positives if using the raw wiki source as input.
Sites like Wiktionary can be linked to without it looking like an external link (with the "up arrow"). Example: a reference to a misspelling on Wiktionary: [[wikt:compatability|compatability]]. Result: compatability. Note that the "|" is always necessary. Otherwise, "wikt:" becomes part of the link text.
To get several paragraphs in a list (indented content), add an HTML break (<br/>) after each paragraph (and do not add hard line breaks). For separation, use more than one break (though this may or may not violate the style guide). A new paragraph. It goes on. There is another paragraph. And it can really be very very long, continuing for sentence after sentence. This and the next paragraph is separated by an empty line.
The last paragraph in this list item. It ends here.
Writing better articles has a section, "Inappropriate lists", on when to use list and when not. It also has a section on the use of rhetorical questions, gender-neutral pronouns, providing context for the reader, stating the obvious, lead sections, principle of least astonishment, spelling ("Articles with good spelling and proper grammar can help encourage further contributions of well-formed content"), and weasel terms.
See Wikipedia:Database download for access to downloadable content of Wikipedia. This article contains actual download URLs. For example, the English Wikipedia is about 6 GB (27 GB uncompressed).
External links instead of references. 2011-01-19. Examles: Widgetbox and Wavelet packet decomposition. See also another Help Desk entry, "Problem of external links in body of articles" - "WP:EL prohibits inline external links from being added to the body of articles; they're supposed to be used only in the "External links" section of an article and, of course, in references properly enclosed between <ref> and </ref> tags. ... The most common cleanup template would be {{External links}}, but there is also {{Cleanup-spam}}. ... When I come across this problem, I always just strip them out by hand, converting relevant links into either references or moving them to the external links section, but most of them I just convert to either plain text or remove entirely.
User/page statistics tool on toolserver.org/"tparis" is broken. The edit counter was broken. (2013-06-01). The new URL is http://tools.wmflabs.org/xtools/pcount/index.php?name=Mortense&lang=en&wiki=wikipedia, but template userinfo (oruser_info) has not been updated yet (2013-06-03).
1. CANopen. Addresses the reader directly - "You can transfer up to 8 bytes (64 bits) data per one PDO" (several instances, for instance near "The Process Data Object protocol is used to process real time data"). Mark template for this? Does the Manual of Style (MOS) address this problem? -Yes! From Second-person pronouns (MOS:YOU): "Do not use the second person (you, your)"
Wikipedia:Typo Team. An organised way for correcting spelling and grammar. It currently has about 1200 members. The page also includes recommendations for edit summaries, links to word lists (e.g., List of commonly misused English words), and a description of spell checkers in web browsers (they are apparently ubiquitous in all major web browsers).
wikEd, an in-browser editor (requires JavaScript to be enabled) that can be enabled in preferences, near "alternative full-featured integrated text editor". It seems to enable find and replace with regular expression support. It includes canned edit summary text, fix common typos, conversion of HTML code to wikicode, and jump to headings. Possible downfall (e.g. for repurposing): "wikEd relies on the browser-internal rich-text editor" and "wikEd replaces the normal text area with its own separate rich-text iframe"
