IMO, most (not all, but most) bad trips can be completely negated by excercising a little foresight. If it's your first time and you don't know what to expect than make some plans to make sure everything is taken care of. Have some friends tripping with you or even a sitter, have food if you want it, create a welcoming space where you won't have to worry about cops or weirding out the neighbors. Plan to have some music, or some art supplies like pens or clay. Make sure you have some options of things to do or look at so you don't end up bored. Maybe take a walk somewhere peaceful, and make sure you don't have to drive anywhere.

Take the phone off the hook and commit to your trip.

Maybe eventually you won't need to take all the precautions to trip, since this is your first, just don't have any unfinished business (homework, bills, bad relationship) that could come to mind and trip you out in a negative way.

Listen to your favorite music, go through some personal affirmations and make sure to enjoy the journey.