This is a difficult question because if this is not in your nature, it is tantamount to asking how to change your personality. To be the life and soul of a party suggests plenty of confidence, good knowledge of most of the party goers, a charismatic personality and a lifestyle the contains lots of humorous or lively incidents to relate.
How many of these can you offer? If you fall short on most of these, it might be best to depend on showing interest in those you speak to, a readiness to pass around food, and offer some new interesting information. Also, where you can introduce one party member to another that you already know, this helps evryone to feel more at ease.
If you want to become the “life” of a party, you first have to get people to notice you are present at the party. How do you do that? Be social; start up a conversation with someone or join a group of people already talking together. Don’t butt in but find a way to get yourself included in the conversation. You could also try to encourage the partygoers to try a new dance move or bring some new music people may not have heard yet.
Another way is to take something to the party that people will want to talk to you about. For example, you could bring a clever gift for the host. If the party will involve alcohol, bring a new bottle or wine, or maybe some Jell-O shots or pudding shots.