The best start before you start using Rogain is to use a DHT removing shampoo that will remove the buildup from the hair follicles. DHT is a byproduct of testosterone which is what causes the thinning hair and the death of the hair follicle.
Rogaine only works for the balding in the back of the head and not the front, so the sooner you can stop the front follicles from dying out....you will also get the benefit of alot of those follicles that aren't really dead yet....but weren't producing alot of hair...back into action.
I've been using Nioxin for about 13 years now and it stopped my hair loss in my late 20's. I'm 40 now and my balding in front hasn't gotten any worse.
I highly recommend this for all men whether you are balding now or not..
http://nioxin.com/en-US/why-nioxin/about-us-page.aspx