I don't think personality is something you get. I think it's something you already have. I think the best thing for anyone is to just be yourself (unless "yourself" is in a nasty or sullen mood, in which case try not to act sullen toward other people).
I think if you just be nice to people and be yourself that's all it takes. Most people will tell you they don't particularly like people who try to fake a "great personality". If you're quiet by nature (for example), just be your quiet self (and yet nice to people too).