During my studies a while ago I stumbled upon a technique where a group of practitioners would pool their energy. This being they would all direct there energy into a single space, and then they would send it out all at once, allowing the spell to be more powerful than any one of them could do themselves.
Have you and your friends sit in a circle. Direct your energy with your intent into the middle of the circle. At the spells end have all of you release the combined energy into the universe.