The hand sign is generally enough. However, if you use a formal bow, you must bow lower than the teacher, and your eyes should always face downward as a sign of trust for your teacher. Never forget your teacher's birthday, or special holidays such as Chinese New Year. A red envelope is usually given containing money. Usually a gift is not given since it may be a gift that the teacher has no use for.
Money is the hardest thing to give up and is the most useful, so a money gift is always best.
The amount depends on your means to give. Always wear the proper uniform and be sure it is clean and pressed. Always bow when entering or leaving the training area. Always pay proper respects to the higher levels in your Kwoon by calling them by proper title. Always pay your dues on time.