The simplest trick is to first establish a baseline. By that I mean whatever you eat that keeps you as you are right now. Then you tweak and change it. To gain add, to lose remove.
Bulk, to me, means to add mass. Meaning muscle but nor lean - some fat too. That's fine for me cos I'm all about the weights moved but others might want to be leaner.
So, by adding a single protein and carb shake or small meal I would, over time, gain mass. PED's speed that process up. Training, of course, needs to be added to as well. My bench wont get better or bigger if I'm not adding reps or weight to the bar. Ergo my chest and arms wont grow either if my bench doesn't go up.
It sounds simple cos it is. The hard part is lifting more when you ache and are tired and eating another meal when you're not hungry. And, course, we only do this cos we want to. We rarely NEED to.