Firstly you want your description to be well-polished with no grammar, spelling or punctuation errors. It needs to be the right length and the game should have no pornographic material.
For images you should use only the best your game has to offer. The first required three or four must not be either game over or title screens. They must each be different from each other (that is, not all of the same map with just a little bit of different text) and be of good quality - that is, mapping and graphical usage must be of a high enough calibre that it is considered good.
If you're not sure of that, ask in the Screenshot thread whether it's okay and pay heed to what it said there. Again, no pornographic or high-rated images allowed.
Lastly, be patient. It takes a while for the Submissions Staff to have the time to go through each and every game and make sure of their quality - they have a life outside of the site, after all. If after a week of waiting you're still waiting to hear something back, send a polite PM to Deckiller.
If your game doesn't get accepted you'll probably receive a small note about why - usually something like "graphics weren't up to site standards" or "description needs working on". In that case just work on refining that issue and then resubmit with updated data.