Do what thou wilt shall be the whole of the Law.
"How would I go about determining which energy to invoke?"
By correspondences. Check Liber 777.
"Could you expand on that for me please brother? Lets say I wanted to invoke positive energy to help me with monetary success?"
You could do that, but it wouldn't be much good without some experience. Also, check Liber O. (Hell, check all the Libri. 😆)
Love is the law, love under will.