Business & farm

So just to confirm, I can claim expenses, even though I didn't earn any income? I was told 20 years ago when I started, that as an actor, in order to claim expenses you had to prove income (even if it was only $50), and I've operated under that assumption ever since. If that's not the case, great to know! So - how do I prove that I was actively looking for work even though I didn't get any? Do I need to have documentation of any kind? How would I prove to the IRS that I was seeking work, and didn't quit but am still trying to claim expenses? Or is the fact that I've had regular acting income for 20 years enough proof?