Always accept favors and kind gestures and free stuff when people offer. There's a phenomenon in psychology that people tend to like people more when they have given them something or helped them in some way. So the next time someone offers to buy you lunch or something like that, don't keep telling them no to be polite, just say, "Oh that's kind, thank you very much!".

In other words, giving to others is good, but don't be shy to take when others want a chance to give as well. It actually makes people like you when you take what they offer.