1) If the fold is important to the fundamental structure of the model, precreasing is generally the way to go. If it is a shaping fold, though, generally precreasing isn't necessary. You will start to get the hang of it as you fold more.
2) Definitely help it along by pinching it. Folds don't just magically reverse themselves when they need to be

As you get more experienced you will develop your own little methods of performing certain folds-there is no prescribed formula as to exactly how to do every fold, but there are easier and there are harder ways of doing them-you will find them out on your own soon enough if you keep folding.
3) It takes a good feel for the paper to work with small details by hand. Don't expect them to be perfect-small details are very hard. You can also use tweezers or a toothpick if you feel the need, but, in my experience, they generally aren't necessary. I try not to use tools like that unless I'm doing something REALLY small (i.e. small details on dollar bill folds).
Good luck and happy folding!