When do you draw the line between being available and your availability being taken for granted? I have always had that problem. I am the kind of person that can do anything for someone I care about, someone I call a friend. It never ceases to amaze me how I always 'give the benefit of the doubt' to people I know are just taking advantage of me.
The truth is we all take advantage of each other but in varying degrees. I know that I love being needed and this is perhaps the reason I always want to be there for a friend when he/she calls.
The fact is when you are always there for someone, you would always be taken for granted no matter what. Live your life without necessarily trying to bend over backwards pleasing people. Its hard to do this but of what use is it pleasing your friends at your expense, without them appreciating? The resentment that builds isn't worth it.
Learning to say no is indeed the first step. It is impossible to always be there for someone...and when you find your self in such position, then you know you are killing yourself slowly. There is nothing wrong in saying 'I would like to help you but I am sorry I cannot' or 'I am indisposed at the moment' or something of that nature.
I still have not achieved that delicate balance but I know that I am not interested in being anybody's foot-mat. If it is not convenient for me, I would say so and I do not care how you beg and plead.
Remember the law of diminishing returns.