People keep talking about how to tell if a spell will work or not. In truth, the most trite bit of doggerel can be an excellent spell. Where most spells fail, is in the belief of the Caster in the spell. You can have the strongest Will in the world, the best spell written by a powerful Witch and worked successfully countless times by many different people, but if you harbor one tiny doubt, it wont work for you.
Before you do a spell, visualize it as already successfully completed. Don't think I'm going to get such and such because I've done this spell, instead see youself as already having it. Believe completely and without doubt that your goal has already been acomplished and it will be. Believe in your ability to work Magick and you can.