Music: Listen to it, play it, whatever. Music is great when you're high on anything. Make sure to listen to music that you like and that won't put you in a bad or agitated mood. Try going to a show or concert. If you play music, you're in for a whole new experience. Try it all.
Make a Plan: If you have a plan before you start your trip you're less likely to end up confused and disoriented. It's good to have an idea of things you want to do. Like painting, playing video games, maybe even cleaning. The more productive you are, the better you'll feel. If you're new to psychedelics pick simple tasks, because it's easy to forget how to do complicated things. And make sure you have everything ready to go before hand. It's not easy look around for stuff when your sense of space/time is disrupted.
Think Happy Thoughts: Staying positive is key. Don't let yourself go to "that place". You all know what I'm talking about. No sad thoughts, no thinking about past regrets, or any of that bullshit. And remember you are winning, people love you, and there's always someone uglier than you are. Have fun.
Hang Out With Friends: This is the number one rule of humans in general. We suck at being alone. Make sure you're surrounded by a cool group of people who love and respect you. If you remember this nugget of golden truth you'll have nothing to worry about.
Lie Down Outside: If you ever feel like everything is getting out of control, walk outside, lie down, and stare up at the sky. You might think you have problems or you might just think you've tripped yourself retarded, but when you're looking into the vastness of the universe, bad thoughts slowly melt away.
Cleanliness is Next to Godliness: It's a lot easier to stay in a good trip if everything around you is clean and organized. If you're going to be tripping in your home. Before you start, take a shower and tidy up. A little goes a long way.
Talk: Your brain is going to be firing on all cylinders, the best way not to get overwhelmed is to talk to your friends. Talking to other people who are tripping with you is a lot of fun. Though you might find yourself spilling some secrets.
Bonus!!! Make Out Session: If you can find someone to make out with do it. Consider the rest of this optional. Now go have fun.