products that are bad for relaxed hair

I had my hair relaxed by Paul Brown straight perm.  My hair is really thick and really corkscrew curly (before it was relaxed). My question is, what products do I want to stay away from so that my hair doesn't curl up again before I have to get it relaxed again in 3 months?  Does either shampoo or conditioner make chemically relaxed hair go back to its original state if the product is used a lot?

Sry, I don't have any pics.  This straightening is great, tho it did take 2 treatments to get a lot of the curl out. I was able to go back a week later and get it done again. Now I get it every 3 months. I think Paul Brown relaxer is one of the gentlest relaxers since it doenst have lye--it has thiolygate or whatever its called.