getting unstuck
Some things to try when you feel like you are stuck:
Visualize!
Draw a picture - really draw, not a schematic (a schematic is for solving).
Conservations laws
Limiting cases
Go for a walk
Dimensional analysis
Guess and check - sometimes figuring out how to check is helpful.
Act out the problem - try it! Experiment!
Find smaller parts of a large problem.
Simplify the problem and solve that - the infamous "spherical cow".
Work backwards - when you know the answer, but not the route!