For starters be sure that the 'chemicals' you add come from a food grade source such as the LHBS, a mail order brewing supply house or the super market. The things you will want to experiment with are plain old table salt, gypsum, calcium chloride, phosphoric acid and lactic acid.
It used to be quite common for drinkers to add table salt to their beer at the bar. It has the effect of.... well try it and see. Most of the bang comes from the chloride and you can add table salt to the point where the chloride's effect gets masked by a salty taste. You'll get the same effects from calcium chloride except that the salty taste is more 'minerally' with the calcium salt. This is a somewhat subtle distinction.
Gypsum, on the other hand, has a pronounced effect on the way you taste the hops. This depends, among other things, on the hops variety. Some people like tons. Some like little or none.
Some brewers feel the finished beer should have a particular pH and add acid to adjust if the beer doesn't hit the target. I have never tried this as my beers seem to finish in the 'recommended' pH ranges. If they were to miss that range I'd blame wort preparation or fermentation problems and doubt that adjusting the pH would fix the problems. If just adjustment of pH is the goal flavor neutral phosphoric acid will be the best bet. Obviously a pH meter is required to tell when you have hit the desired range (or indeed that you are out of it to the point that you need to add acid). Lactic acid is a different matter. It is a major flavor contributor (though it does, of course, lower pH as well). If you are brewing a sour beer (Berliner Weiße, Wit...) you may well want more tartness and lactic will give you that. Just be aware that lactic flavors take some time to meld so add lactic until you detect a taste dfference and then wait a few weeks before adding any more.