Meditate. Meditation is very useful to both new and experienced practitioners, as it can focus and hone one's energies. Meditation also allows us to extend our spiritual grasp and feel and use the energies around us, thus giving us a little more power with our spells.
Meditate before casting, make sure that you've eaten and drank, and got enough sleep. It's hard to cast if you can't keep your head up!
Hope I helped, if you have any more questions, feel free to inbox me.