Don't worry about making a layout that isn't shit - I can almost guarantee you, no matter how hard you think things over, it will be shit. The best thing you can do, as someone who is new to TF2 map design, is make something crap and understand why it is crap. Then, change the map to make it less crap, lather, rinse, repeat.a layout that isn't total shit.
There is no design bible on how to make good maps, because writing such a book would be impossible - everyone learns and understands differently! It's important to understand design in a way that makes sense to you, and that can only be gained through experience.