The important thing is that -you- know what you want your spell to do and that you clearly let the Universal (including your gods and goddesses) know. The longer and more drawn out your wording gets, the easier it is going to be to lose your own intentions.
Instead of trying to elaborate with a long, detailed paragraph like:
"Today I got my test back and the score was not good. I thought I did well but I was wrong. Please grant me your wisdom to aid me in my next test. Please send me your power and help me do well. I really need to do better in this class, please make it so..."
Try to condense it all into a few short powerful ideas like:
"This test must be lesson, never let me forget. Grant me your spirit that I shall do better next time. Aid me now in my time of need."
Use terminology and phraseology that resonate with you, and make it powerful. Remember that some terms (most "command" words) are more than just words.