Legal methods for reducing commission tax?

I work in IT and I get paid my normal salary every month and on occasion. I'm also involved with projects where I earn commission. I don't actually know how my commission is calculated, but I'd like to know how I can get more of my commission paid to me instead of being taxed so highly. My Minimal expenses are i.e. calls and some driving around but I don't claim for it because it's usually a very small claim.

Since those are the only expenses you incur, unfortunately you can only claim them in order to decrease the tax on your commission income.