Before casting magic I take several minutes to myself and focus on the spell I am going to do and what my intentions are. I visualize the spell having worked and my end result being true.
Meditation is always great, focussing on your intention. If you follow a certain deity you could pray to them and ask for help. If you want to get rid of any negative energy you could ground. There are lots of articles on this site that could help, you've just got to search for them.
I suppose the quick answer is 'prepare for the magic spell'.
Of course the less cheeky response can be a tad more involved though. How much you do before working magic is ultimately up to you and what you feel is necessary based on the complexity of what you want to accomplish. It also depends on how much of your time energy and will you are planning on comitting, so most of the stuff I'm suggesting here can be considered as optional.
'Preparing' for magic usually involves first being sure you understand what the goal is of what you are preparing to do. And confirming that the different aspects of the spoell mesh with what you want to happen as specifically as you can. For example examining the wording of the spell and/or what you are calling for. It also usually involves a period of self reflection and evaluation on a moral basis of the spell. IE; Not only is this what you want to do, but is this the way you want to do it, and is it something you -should- do?
Other helpful things in preparation is going over the different pieces of the spell process, to make sure you understand the function of the different steps of the spell. it can be inportant to be aware of where in the spell you are laying protection, or establishing your intent, or releasing that intent outward. That lets you further tailor the working by finding more personal and familiar symbols that you can use to connect yourself to the purpose of each step.
And of course study of the spell and possible influences so you can tailor still that too. For example selecting a time of day that favors your intent. Or exploring the available options of where to perform the magic. Basically looking into ways ou can maximize the potential effect of the working.
Even just before starting the working, it can be helpful to meditate a bit, or listen to some music or read some journals. Do a few simple activities to get yourself into a magical mood and frame of mind. Bathing to symbolically wash off the mundane is a good practice. As is performing a smudging or sun/moon bath to cleanse yourself and your mind and get yourself focused. Even doing something as simple as making yourself conscious and aware of the specific purpose to each spell component as you gather them together can go a long ways towards kicking yourself into a magically focused mindset. Some add a wardrobe to the mix, having specific clothing set aside to be worn only during ritual times as a sort of uniform to signify the transition into a time of magical attention.
