Treat others with respect.
Your beliefs, hobbies and reputation are some of the few personal things that you have. No one wants to associate themselves with a pompous prick who is only interested in themselves. Any business relationship and friendship is based on what value it brings. No one wants to be used, treat others as a you would treat yourself rather than a means to an end.
This will prove to be useful in the long run, as people have really good memories when it comes to getting screwed over. Just because you may not necessarily need someone now, how do you know that they won’t be useful to you in the future? That is why it is always important to be courteous and treat others with respect.