I would recommend having at look at their site(/s) and having a look at their todo lists and bug tracking systems to see where you can help out and just try to

I would recommend having at look at their site(/s) and having a look at their todo lists and bug tracking systems to see where you can help out and just try to write a patch for it in their preferred method and see what happens. For Example: for Mediawiki you could look at their bugzilla and find the open bugs with the "easy" keyword (http://bit.ly/3SbYJG http://bit.ly/3SbYJG) and try to write patches. And also you can help out on their Chatrooms/IRC Channels, Message Boards, Mailing Lists ect