Contribute what you know or are willing to learn about. One of the things that makes the Wikipedia great is that anybody can contribute, however this creates a problem to whether the information posted is true, but another thing that makes it great is that it encourages Wikipedians to stretch their interests and learn about new things, so that they can add to the 'pedia. A third great thing is that it's so easy to create new articles and to learn to wikify articles.
Some users see the ease in which new articles can be created as problematic. Many users know something about a subject, but few have exhaustive knowledge of the subject they are writing about. That leads to users creating stubs (very short articles) that need to be extended by someone with more knowledge before the article can be useful to anyone. This irritates some because it leaves a lot of unfinished work in Wikipedia.
Other users have diametrically opposite views of stubs, that an iterative style of development can indeed be beneficial. They feel that the problem described above isn't a problem but a part of the normal wiki process, that a not-so-good article is better than no article at all.
(an alternative phrasing)
Whenever you create a new article, always try to make it as complete and comprehensive as possible. However, an article that is seriously incomplete but a useful start is welcome, too. But first check so that the article you are about to create doesn't already exist in Wikipedia. Or maybe your new information would be better placed in an already existing article? If you are a newcomer to Wikipedia, concentrate on adding content; do not worry too much about formatting. If anything your edits should cause other editors to get involved by reverting and or further re-editing the article (see Wikipedia:BOLD, revert, discuss cycle).