The issue with belief is that you can't force yourself to believe in something; beliefs aren't really conscious decisions. You don't consciously decide about every single thing you believe or disbelieve, and you can't automatically say to yourself "OK, I'll believe this now", because you'll still have thoughts in your head and an overwhelming feeling of "No, I don't think this is true."
I do what Dillon does; it's almost like a scientific approach. If I try a ceremony, or a ritual, or whatever, and there's no noticeable effect, then I'll make changes, and see how they impact upon it. That's why there's such an emphasis on keeping a journal specifically for your occult practices, just as you'd do with dreams.
For me, I don't neccessarily believe fully that magick, in one form or another, is definite and fully exists or anything of that sort; I don't have the evidence to make such a claim. However, I don't fully throw it out, or find it silly, or anything like that. I hold the view that there's at least potential, and that it's a possibility, and I'm exploring and experimenting and studying in order to find out what works for me and what doesn't, among other reasons.
Me not fully throwing it out, and accepting and approaching it as being a possibility and something to be explored seems to do the job for me. I don't really like the whole idea of "believing is seeing", not only because I just can't force myself to believe things for no good reason, but also because I don't think that and yet I can still see some sort of connective results and effects; that then brings up the "scepticism of ones own experience" thought, and, further, questions whether it was an external experience, psychological, etc.
Even if spells/rituals/whatever's effects *do* turn out to be fully psychological, and applying the placebo affect, among other affects, then so be it; if it works, it works. It doesn't make it any less awesome and inspiring to learn more of it and to keep going deeper down the rabbit hole, in my opinion.