First, make a list of everything you know. Then,
write an article for every item on that list. If, for some reason,
this is not practical, here are some other tips to help you get
started.
Choose a topic that is of interest to you. Find
out what has been written about that topic so far. Make improvements
to the articles that already exist. Fill in the gaps by creating
new articles on aspects of the topic that have not been covered
yet.
Visit a Random
Page. Find a link to an article on that page that hasn't been
written yet. These are the links that have little blue question
marks after the words. Click on the question mark, and add something
about that topic.
Write about something you don't know
about. Use this as an excuse to research a new topic. As you learn
about it, write what you are learning here on Wikipedia. This
is actually a good study aid because it forces you to take notes,
to organize information, and to put what you've learned into your
own words.
Make a project! Take a book and write a thorough
chapter-by-chapter summary. Make pages for all the characters.
Or do this with your favorite fictional universe (Star Wars, Middle
Earth). Pick your favorite actor and review all of their movies.
Pick your favorite city and build pages for all its best attractions.
Find a big topic (like World War II or Chinese
history) and create a main page, and all the subcategory pages.
List all the topics that should be covered for a complete treatment.
You don't have to write articles for all these topics. But if
you build an outline and list everything that needs to be filled
in, eventually someone will come along and start filling in!
You don't have to write to contribute. Edit pages
for spelling and grammatical errors. Remove nonsense when you
see it. Correct false or misleading claims. Wikify words (turn
them into links). Find redundant pages like Chicago and Chicago
Illinois and combine them.