Before attempting to perform magic, you need to get into the right frame of both body and mind and cleanse away any doubts, demons or spiritual impurities that might distract you or make the spell go awry. Ideally purifying yourself should be a ritual in and of itself, and should leave your body relaxed and your mind nuclear.
Bathe. Take a long bath, getting your skin completely clean and soaking the tension of our your muscles. Dress appropriately. If you have robes or other special garb for doing magic, put that on. Otherwise pick simple but formal clothes that feel light, comfortable and clean. You are asking the divine forces for a favor, so try to dress with a certain amount of reverence. If there won't be anyone around, some wiccans swear by performing magic in the nude. Meditate until your mind is clear. Do some basic deep breathing to improve your focus and discard distracting desires. Anoint yourself with the proper oils. Different essential oils can be used for different purposes, so if you like find one or more that seem appropriate and dab a little with your fingers on your forehead, and perhaps your hands, hair, face and chest as well.