You're probably more likely to reach the front page when you're not really trying. I know that sounds like a cliché, but that's how it works for me.
But seriously, it doesn't matter that much, does it? Just make memes you like, or that you think other people might enjoy, and have fun (that would be my advice for whatever it's worth).
Also, a quick and easy shortcut to get your sense of humor seen on the front page is to make funny meme comments on memes that are already on the front page.
