How can I be more outgoing without being immature?

dont be a retard. that's pretty much it. be talkative and attentive, don't talk super quiet but not LOUD either. just act like he's one of the girl friends =P it might make you feel more comfortable

Be positive w/out being bubbly and ignorant.

Be cheerful at the right times and try to make people feel better.tactfully

Really an outgoing person in my mind is someone who is always on the go and makes me want to go with them. I don't see it as being immature like in HS but rather someone who is the life of the party with out over doing it. You can suggest doing something constantly and inviting people to come with you but also listening to what people have to say about what they want to do. Someone who is flexible but is a motivator to others. That's what I would suggest. It's hard and you have to push yourself first but after awhile you'll get the hang of it and you can be one of those people that everyone wants to hang out with. I for one would pick out one or two people that act they way you want too and see what they do and try to emulate that into your own personality. You have to try and make it your own though that way your are being genuinely true to yourself.

genuine compliments
don't make them up or seem fake.