Great advice. Yeah there are a lot of us who feel the same as you. I think firstly you have to like yourself. Don't put yourself down amongst other people and of course don't put them down. Try not to come across as too needy but be interested in other people. Get out ( meetup.com is good) and do stuff you enjoy doing. I like myself and i would want to be friends with me haha, if other people don't that's their loss. Don''t think too much about what YOU think others think of you. Challenge yourself to do things outside of your comfort zone. Think, What's the worst that can happen if it goes wrong. Normally if it does the consequences are minimal and far outweighed by the satisfaction of doing it. People like confidence in other people and the more confidence you get the better you will feel and the more people will enjoy your company.