Too be honest, it really doesn't matter who's spell you use. But you should know which spells are real and which spells are fake.
Its better to write your own spell because you have more chance of it working. Things is suggest you do before casting.
Meditation(set an intention)
Preparation for the spells(candles, what time you're going to cast it)
Then when you feel ready and prepared get read to vast your spell, but make sure you visualise the outcome.