Well it depends what you want to do on the site. But the thing that helped me most, that I would suggest, is just to comment on other people's memes.
Why?
A) Making a funny comment that builds off someone's meme is easier than coming up with something from scratch.
B) If your comments are interesting, people might come check out your memes too.
C) Sometimes the comments you make will give you ideas for memes you can submit (or sometimes the comment works enough by itself that you can just submit it as is).
Anyway, my suggestion is - comment, comment, comment.