No matter how experienced you are with tripping, please pick a few (any) of these Essential Links and read them from start to finish... unless you've already read them.
Trip-toys can greatly enhance a trip, especially in a group setting. These "toys" can include anything from Music visualizations to blacklights to glowsticks.
A "Trip Sitter" can be a very helpful person to have around especially if this person is naturally laid back and has experience with psychedelics and trippers.