Magick is an art, and great artists steal. You can make up your own rituals, but I am of the view that if you do not study and understand the methods of other, much more experienced occultists, you will end up making mistakes or leaving out processes that others have found to be quite effective for no real reason (aside from perhaps being too lazy to read and learn).
Magick is a very personal art, but I often see the idea floating around here that using other people’s methods is somehow “bad” or not as good as something completely made up by you. I think this is ridiculous. Imagine if none of the world’s scientists ever shared their results with each other - everyone would just be doing the same experiments, making the same mistakes, wasting time for no reason (this is actually more of a problem than you may think nowadays in some fields).
I suggest learning from a book like Demons of Magick or Evoking Eternity or Orlee Stewart’s Ars Goetia. Once you have an idea for how other people are doing things, feel free to do whatever you want to do.
Or just do whatever now, and if your results are good enough for you, then who am I to impede upon you.