EXPERIMENT!!!
If you don't have any ideas, don't worry about them. Try reading some more advanced tuts to get the ideas going! The best way to learn is to experiment for yourself, so just muck about with hammer for a while... discover some of the more advanced entities and how to use them!
How to use func_trains, ambient_generics, func_ladders, trigger_once/multiples, monstermakers, env_beams... most are actually quite simple to use, you just have to "discover" them!