Self-esteem is generally a good indicator of how you handle rejection. If you're very secure, being left out won' make such a dent.
Welcome advice
Reach out
You won't be included if no one knows that you're around. At your home, don't hole up inside by yourself. If your neighbours are out playing catch with their kids, go out for a chat.
Advertise your intersts
Let people know that you're interested in doing things with them.
Assess your style
If you're letting people know that you're interested but you're still getting left out a lot, the problem may be your style.
Be a better listener
If, on the other hand, you tend to dominate every conversation, otherpeople will start to resent it and begin to exclude you. So before jumping into a conversation, listen first.
Interview others
Changing the topic to one that focuses more on you and your interests may turn people off.