Tax time for one whose friend does the trading

Hi folks, first post here. I am not yet a trader but hope to be someday. Got me a wee question on taxes in the USA. I have invested with a friend over the past year and a half. He is an excellent forex trader and gives me 100% annual returns. Now I am wondering the best legit way to pay taxes on the return since I am not a trader? Let me know of any IRS Forms? suggestions? trade secrets?

Other info: I was thinking that until my returns surpass my principle investment then I can simply show that the outgoing and incoming monies balance on my bank statement, let me know if this is alright.