Well, how much do you water now? I'd mix up enough 1/4 strength solution for the first week and if the plants do well then try 1/2 strength, then full for the third week on.

Oh, and some plants tend to get bushy while others dont. You might just have a strain that doesn't branch much. One thing that's easy to do and should get you some more branching is LST(tying the main stem over so the light's exposed to the bottom). Generally LST is used in veg but the first two weeks or so of flower you can use it as well. Check this, this, and this out for how to LST.