Well if you've studied what magick is and what is/isn't possible with magick I feel it helped me when I was new.
I would start with basics like grounding and energy manipulation to get a feel of the energy used in spells.
Once you get a feel for the energy try casting a simple spell, something attainable, and measurable. Then keep a journal and write down anything you notice. [example, cast a money spell, every time you find a coin, get offered extra chores, get extra shifts at work, or other money making gains occur]
Personally, I never struggled much with believing in magick, the explanation of it being similar to science, and how it was an energy that worked with nature to help bring a desired change quicker just made sense to me and connected to me on a deeper level so I never tried testing spells [i mean, I've tested spells I've made, but testing to discover magick was real no] I spent a year studying magick and researching the history of witchcraft and I felt rather grounded by the time I tried casting my first spell.
I would like to issue a warning to you and those who read this post: often times believing enough will cause your mind to make up some of the way or attach special significance to things that are ordinary in nature. You need to learn what is the fancy of your mind, and what is real.
A good way to test this is to go outside for a night. Or simply go to an area where you can be by yourself, in complete darkness. You’ll be interested in what your mind will make up to get you out.
This does not mean to believe. I am simply saying that it would be unhealthy to believe a rock will fall to the sky (a kvothe reference ) repeatedly being proven wrong. Stick to paths already wandered, and try to find a mentor to help you. Keep a balance with yourself and you will be better (though not necessarily happier)
