What do you think is the best way to make a definite person your friend?

Always be yourself. Minor adjustments are acceptable, but in the most part just do what you do. You can't hide under a mask forever and if you want to make a certain person your friend, he'll find out about what you're hiding sooner or later. As for the favour. I think that they make a connection and they define a relationship. It depends on the friendship that you have. Favours should not be THE WAY to maintain a good relationship. It should be the way to show the other person that you are their friend. There are other ways, but that is a good one also. :)