While words, tools, and a lot of the theatrics involved in a lot of magic aren't necessarily required they do help a lot if you are a beginner and need help focusing. They're also pretty great for adding a little extra kick later on because you can psych yourself up for it.
Back to the original post though, if a spell claims to do something that isn't physically possible it won't work. Spells to summon an animal familiar to you will not work, familiars are spirits rather than animals. Spells you don't believe will work, won't work.
The best thing to do is to start small and work up. Use whatever tools you have and feel like you need. Push yourself a little at a time, take notes and see what works best for you. This isn't a science necessarily, but treating each spell as an experiment and keeping track of your results helps a lot in my experience.