Suppose you want to write a first-rate or even perfect Wikipedia article that deserves to be listed on featured articles (those considered by consensus to be Wikipedia's best articles). Start by trying to meet as many of the featured article criteria as you can. Here's more guidance on how to do that.
Once you have decided on a topic, use Wikipedia's search engine to find out what related material we already have. That way, you discover what already exists and can later create good links to and from other relevant articles.
How to get started
You may think that you know enough about your topic, but it's possible that others know more. Do a search on Wikipedias in other languages, on Everything2 , look at the first few hits from a search engine such as Google , and read the relevant articles from an encyclopedia; these sites all may help you: Encyclopedia.com (free), AllRefer Reference (free), Encyclopædia Britannica School & Library Site (free in most libraries).
It's a good idea to visit an academic or public library to have a look at the standard references. It is generally considered that the best Wikipedia articles should cite the best and most reliable references available for the subject. Those may include books or peer reviewed journal articles.
Finding relevant articles
There are several ways to find and retrieve articles online, without having to leave home. Google Scholar  is an excellent source for finding sometimes free online peer reviewed articles; note that the free articles are usually marked with "View as HTML."
Many libraries have agreements with database providers under which library users with current library cards can connect for free to the databases from their home computers — that is, the users do not need to be physically present in the library. Check with your local public or academic library to find out which databases it subscribes to, and whether they have a mechanism in place for remote access. Some high-end databases (like InfoTrac and ProQuest) even carry scanned versions of articles as they were originally printed, in Adobe Acrobat's Portable Document Format.
Examples of comprehensive general interest databases that may be available through your local library include:
- EBSCO - Full academic version (Academic Search Premier) has full text of millions of articles from over 4,600 sources. Full public library version (MasterFILE Premier) has full text coverage of about 2,100 sources.
- Infotrac - OneFile database has full text of about 50 million articles from 1980 to the present. Widely available at academic and public libraries throughout North America. Operated by Thomson Gale (formerly Gale Group), a subsidiary of the Thomson Corporation.
- JSTOR - Has full text of articles from several hundred scholarly journals from their beginning to approximately five years ago. Operated by a consortium of universities.
- LexisNexis - Full version (available only to lawyers and journalists) has millions of full-text articles (from magazines, journals, and newspapers), court opinions, statutes, treatises, transcripts, public records, and more. Academic version (available at many universities) offers large subsets of the legal and news databases.
- ProQuest - Full version (ProQuest 5000) has full text of millions of articles from 7,400 sources as far back as 1971. The ProQuest Historical Newspapers database has images in PDF format of all issues of the New York Times published between 1851 and 2001. Most libraries offer access to only part of the huge ProQuest database, through account types like eLibrary, Platinum, Silver, Gold, or Discovery.
Academic libraries often subscribe to special interest databases with in-depth coverage, of which there are far too many to list here.
Finding relevant books
If you are doing in-depth research on a complex or controversial subject, you should obtain relevant books in addition to articles. If the subject is of historical interest, you may have to visit a library to obtain articles that were published prior to 1980, since few online databases contain such old articles.
To find books or periodicals stored as bound volumes, the best place to start is with the catalog of your local public library. If you have searched the catalogs of several local libraries without success, try searching library "union" catalogs. With one search in a union catalog, it is possible to determine what books are available on a subject in an entire county, state, province, or country. The largest union catalog is OCLC WorldCat, which claims to have worldwide coverage, though most of its member libraries are in North America.
Only by citing the best sources in a field can a Wikipedia article be taken seriously by its critics. For more on this issue, see Wikipedia:Verifiability.
If you are creating a brand-new article (see m:Help:Starting a new page), there are a couple of naming conventions that you should follow.
Start your article with a concise paragraph defining the topic at hand and mentioning the most important points. The reader should be able to get a good overview by only reading this first paragraph.
Then start the article properly. See our editing help for the format we use to produce links, emphasize text, lists, headlines etc. Make sure to link to other relevant Wikipedia articles. Also, where appropriate, add links in other articles back to your article.
You cannot simply copy-and-paste from one of the external resources mentioned above. See Copyrights for the details.
It's often a good idea to separate the major sections of your articles with section headlines.
For many topics, a history section is very appropriate, outlining how thinking about the concept evolved over time.
If different people have different opinions about your topic, characterize that debate from the Neutral point of view.
Try to get your spelling right. Wikipedia does not yet contain a spell checker, but you can write and spell-check your article first in a word processor or text editor (which is a lot more comfortable than the Wikipedia text-box anyway) and then paste it into said text-box. Another option is a program (such as iespell for Internet Explorer) that can be installed on your web browser and used as a spell checker in text boxes.
Keep the article in an encyclopedic style: add etymology or provenance (when available), look for analogies and eventual comparisons to propose. Be objective: avoid personal comments (or turn them into general statements, but only when they coincide), don't use personal forms (I found that...). The Wikipedia Manual of Style can help you with your English. You can post questions about English grammar and usage at the Wikipedia language and grammar desk.
Try to avoid using euphemisms, such as "passed away" for "died", or "made love" for "had sex".
At the end, you should list the references you used and the best available external links about the topic. These references are what will allow Wikipedia to be the most trusted, reliable resource it can be.
Finish the article with a good relevant image or graphic. See Graphics tutorials for practical help on drawing diagrams and modifying images. Many copyright-free images are listed at our public domain image list. Please do not link to images on other servers; instead use the upload page.
One way to get a good article is to bounce it back and forth between several Wikipedians. Use the Talk pages to refine the topic, ask for their confirmations, note their doubts: it is usually interesting to discover that, perhaps from the other side of the planet, after a while, some other contributors can check other sources, or propose different interpretations. The composition of a commonly agreed interpretation is the most important ingredient of a serious Wikipedia article.
It may also be useful to look up your subject in one of the foreign-language Wikipedias, such as the German or French editions. While the English-language Wikipedia is the biggest one in terms of the total number of articles it contains, you may find that other Wikipedias sometimes contain more in-depth articles, especially if the subject is of local importance. Even if your foreign language skills are not particularly developed, you may still glean important information from those articles, like birth dates, statistics, bibliographies, or the names of persons that are linked on the page. If you have incorporated the additional information, please also make the appropriate Interwiki links at the end of your article.
Don't neglect the External links and References sections. The most useful and accurate material you've found with your Internet research might make good links for a reader too. And sometimes there is a standard work that is mentioned over and over in connection with your topic. Mention it, with its author and publication date. Even better, obtain a copy and use it to check the material in the article.
On the Wikipedia, there's a huge tendency for articles to become somewhat bitty as contributors dip in and out and contribute individual sentences or paragraphs. This can lead to redundancy or a wandering train of thought. Even if you don't contribute new content to an article, it's still helpful to rearrange, rephrase, condense and generally improve the readability of a Wikipedia article.