Try to talk more about stuff you saw online or something that your friend sent you this makes you seem more active and social .
Be light and cheery, This makes people think that you are fun and outgoing. Don't be gloomy and act bored. To lighten the mood play some music by the latest artists, people will think you know what music is best. If they don't like the song play a different one that matches their personality.
If people expect you to be on your iphone more than your computer, just type in "Sent from my iphone" at the bottom of the screen :)
Act like you have better things to do. Start going on your Instagram, Facebook, Twitter, etc. at parties. Take pics of the party and post them. Don't sit in a corner and be on your phone the whole time. Get into the mood of the party, take some selfies, videos, or group pics.