try and remember that you arent working with a recipe. its not the mixing of ingredients and the mumbling of rhymes that powers your spellcraft. it's the intent that you imbue each item of the spell with, working energies in the universe... depending on your tradition.. but that's roughly what we all say. you may need to work on putting your intent into your spells, or all you'll ever have is a cauldron of pretty smelling ingredients.
The more you study and understand the more success you will have. As with anything else practice will help you get better. The more you know about the subject, materials, and yourself the better your spell working will be.