There is no trick, and no easy way to do this. You need to manually level the volumes both within a patch (so that turning on/off one FX doesn't cause huge volume changes) and among patches. Just like the real world, some amps are simply louder than others, and each FX pedal has knobs that affect its volume/mix level.

The basic method is to start with your clean tones. Get them all at the same relative level, then move on to the dirtier tones, with your really hi-gian tones last on the list. Since you don't want to change the tonal quality, but only volume, your basic tools are the the Amp Volume (not Drive) and the Mixer. Avoid using the Amp Master Volume, and keep the Device Master Volume at a fairly high level.