start from the beginning. sit and meditate. once you have meditation down, work on visualization, then energy work. chakra's wouldn't hurt either.
for a spell to work you need to clear your mind of all thoughts except the task at hand, visualize the desired outcome so well it seems real, then charge with energy and focus this energy into a direction. the energy you must use is neutral energy found in nature, not the energy in your body. using the bodies natural energy can result in weak spell casting, and draining your energy causing sickness.
the ability to see the future, you might be clairvoyant to some degree. it doesn't mean your spell casting would be better or worse as a result, it's just a natural born skill you should work on developing. there's exercises you could try, as well as teas, and of course balancing all your chakra's will help you as well.