If you are new to wikis, check out the tutorial. Please assist by contributing to or creating any articles whatsoever about the Metro series. All positive contributions great or small will be fully appreciated.
Every wiki has lists of articles that need help. Here at the Metro Wiki we have a special category, Category:Needing Improvement which outlines all the pages that currently need work. These are the articles that need the most attention and any positive contribution would certainly benefit the Wiki. Uploading images is another really easy way to help out, you can do that on the Special:Upload page. You can find a list of useful templates here.
Check out the community portal to see what the community is working on, to give feedback or just to say hi.