How do I balance between respecting my child and not spoiling him or letting him think that he can get his way all the time?

I think showing respect is like treating the child like any other person. Recognizing his/her feelings, giving explanations (instead of "because I said so") for any rules/actions/punishments etc. It is different from giving in to his/her every requests. If he/she is throwing a tantrum in order to get his way, a parent should teach him/her the proper way to ask for something. This does not mean that the parent is not respecting his/her child. Just my two cents worth.

I think being firm is the most important thing you can do. Being firm doesn't mean you are too negative or controlling. You can be firm while respecting your child's space and yet give him or her an indication that they are going against the line you've drawn earlier.