Practice, practice, practice. I've only been messing with this leather hobby since January of this year and am just now getting consistent dye jobs. I'm not saying I do it 'properly,' but I use 3 large sealed cake pans. Light brown, dark brown, and black. Dip until even, buff off the excess and allow to dry - I do all of this outside with a mask on. This is one I'm most pleased with as I didn't think it was possible to get light colors with the dip dying before.
Note that I've used an airbrush successfully as well. My beef was that it didn't have any penetration. Once it got scratched up the color was gone - I can groove a stitch line after dip dying and maintain the same color. Not so much of an issue with an IWB or concealed holster but I wear several of mine on the farm and wasn't happy with how they aged. It's a shame because I think the brush gives the best LOOKING results bar none. I hope this helps some but as with anything your results may vary.