Yes, happycheeks, there are techniques to use. Cognitive-Behavioral Therapy (CBT) uses them, for example. I'm not able to give you the complete package here though!

Here are some quick ideas:

1) Get an affirmation tape and listen to it (positive statements listened to while in a relaxed state)
2) Write down good things about yourself and read them frequently
3) Focus on the positive each day--what can you be grateful for?
4) Get therapy for low self-esteem, etc.
5) As much as possible, work on fixing bad things in your life. No friends? Then get out with other people--maybe a social group, a community group, esp. people you might have things in common with. Be friendly and positive, even if you don't feel like it.....(We all get rejected sometimes. We just need to accept it and move on. Not everybody can realize how wonderful we are! ) That said, are there things we ARE doing that turn people off? Again, the best way perhaps to find that out is to talk to a counselor or someone you know who cares who can be a bit objective...)
6) Get involved with humor and positive things. Read, watch, listen to things that are funny and entertaining and positive.
7) Relatedly, try to avoid the negative. People, topics, TV shows, etc. that bring you down. I don't even go on some forums here, not because I don't care, but because they upset me too much.

I hope these quick ideas help get you started.