Adding salts won't necessarily improve your beer. Some beers contain salts which do contribute to the flavor profile. One could argue that those will be improved if salts are added to RO water but others might argue that they are not. Other beers are made with very soft (low mineral content) water and these are not improved by the addition of salts. But it really is a matter of personal taste. Some people like the taste imparted by minerals and some don't.
Unfortunately, the popular pH stabilizer sold at many home brew stores is ineffective at lowering mash pH into the desired range. It takes acid to do that in most cases.
To get started in understanding all this have a look at the Water Primer in the stickies section of the Brew Science topic.