thank you for this thread, I love it!
I agree with El Jay, sometimes one's life is really very different from most people's, in the last years I managed (with a good dose of patience) to make friends with people who haven't had the intense experiences that I had, but, well, in general my problems are (actually I am not sure these are my issues, if I knew I would have more friends)
1) like Locke says, sometimes social anxiety kicks in, so my mind goes blank, and if there is a thing that I can say wrong, I will say it
2) To cover social anxiety, for many many years now I make an effort to be more outgoing, and sometimes, especially if I am tired, I push it too far and become really obnoxious, back-slapping, roar-laughing obnoxious (I have been told that is not true, but probably I still do something wrong, because some people do hate me at first sight) and, yes, I was also told that I laugh too much in the wrong moments. Also, when I do that, I feel it is really counterproductive, because that is not really me. Vivacious, yes, boisterous, no.
3) Often I don't listen to people with enough attention or talk too much about myself, sometimes it is because I don't really know what to say and I am nervous, other times it could be that I am just too egocentric (that is a problem, working on it)
4) The main problem is that after the first meeting, where people usually find me pleasant enough, I don't know how to go on, when I was younger it would happen naturally, you tell the story of your life, the other person does too, you laugh at similar things, hate similar things, and there, you are friends. Now it seems that there is a restraint, and also I probably have restraints too, and I don't know where to start to get personal, I feel I have too many problems and that would be a burden to people, and some days these problems are so huge that I don't have much else to talk about.
5) I very very rarely meet people who are similar in tastes, education and attitudes, I guess I am a bit of a weird mix
I feel like this list could go on forever, but I guess I'll stop it here