How do you know whether people want you around or not?

Sometimes I feel as if people don't want me around them, as if I am some kind of nuisance. This often prevents me from getting to know people and often saying hi to people I already know due to fear of being seen as too 'needy'. I try to be a kind person and I will genuinely speak to anybody, it just seems that the times that I put the effort in to say hi to people they never put the effort in to say it to me :/