I see many of you are having trouble following the guidelines, so let me simplify the most important ones.
You can post one entry per category or subcategory. What this means is you can post two videos (videos being subcategory of Other) if one is a trailer and the other is a fragvid. What you cannot do, however, is post two hand-drawn pictures.
Subcategories are not set. They're basically a way to enable you to post more entries in one category. If you're good at art and want to enter with more drawings, you could draw one on paper and the other on your pc and name them "drawing" and "digital art", or something like that. Or maps, you can enter with multiple and come up with "vertical cp", "koth" and "most artistic" subcategories. Be reasonable, however, and don't spam your entries.
Thread titles. These are mostly for our convenience, so we can list the entries and divide them into categories easier.
The name should look like this:
"[Category] - [Username] - [Subcategory (if applicable)][name of the submission]"
Categories are listed in the board-specific rules. They're the names in red. Game Content and Creative are NOT categories. Maps, Screenshots and Art are.
A few good examples from previous years would be:
[Art] - [Killercrusher232] - [Sprite Set] - [Blast from the Past Rocketman], where Sprite Set is a subcategory.
[Fake Update Poster] - [a pacifist] - [The iCatching Update]
[Map] - [21Dan] - [koth_friendly]
[PixelArt]-[Melasos]-[Camping]
As usual, the best way to see what's up is to check out previous years' contests. You can find them at the bottom of our forum.