There’s no limits to the number of affiliate programs you sign up for so applying for one today will not prevent you from picking another one later on. In fact, being a member of more affiliate programs simply gives you more options in terms of products to promote plus they’re pretty much all free to join. You can always leave a program if it’s not working out for you or there are no products you want to promote.
Although this article has been written in 2007, now in Feb 2014, I still find it full of great advice and tips. What I learned from this article is that when writing a review I should focus on how this product helped me achieve X instead of simply repeating and enforcing the features and benefits of the product that can also be found on the sales page.