You want to get beyond the stage of using other people's recipes-- you want to really learn how to cook. You want to learn to understand the ingredients, the tools, you want to hone those skills so that you don't have to stand there reading someone else's instructions-- you can achieve your own vision of a dish, because you have learned what to do.
The most important tool for spellcasting is not the cauldron, nor the candle, nor is it even the spell book. It's the mind.
The stronger you can make your mind, the better you will be. It's important to learn how to:
maintain focus for long periods
move at will from one state of consciousness to another
access untapped parts of the conscious and subconscious more easily
hone your sensory perceptions
manipulate energy (raising, holding, releasing, directing)
The way you strengthen your mind is the same way you would strengthen any other muscles-- you have to 'exercise' it.
Believe it or not, common brain teasers and puzzles are a good part of that. Reading is another really good part to strengthen your mind-- think of it as proper nourishment.
There are also psychic exercises* to help you improve your mental abilities. Many exercises teach you how to use all your senses, as well as your extra-senses. They also teach you how to sense and gain control over energy.
Probably the best way to strengthen the mind is the M-word; that's right-- meditation*. I know a lot of people don't like that word, and are not patient enough to master the process, but meditation for the mind is akin to weight training for the body.
Keep in mind, meditation is not all about sitting still, wiping the mind blank and being bored for an hour. There are many different focal points, many meditative techniques, and for those who don't like to sit still there is even moving meditations. If you're going to practice magick, you should consider at least giving it a try.