IMO, the key to getting real power on this shot is the weight transfer. I see guys throw this shot all the time with too much weight on the front foot, or they'll press up off the lead leg when throwing it...... both these habits significantly diminish the power your able to get on the shot. If ya want to really dig this shot in, you have to keep your weight lower and drive off the front foot transferring your weight straight back --- to the rear foot vs. transferring the weight up /
As for the best way to set it up, it's more about positioning than any specific punch or feint. Ideally, you want the point of your lead hip slightly outside the point of your opponents rear hip and your rear shoulder to the left of your opponents center-line (your rear shoulder should be lined up closer to his rear shoulder).
Personally, I think the best way to set it up is doubling/tripling off the lead with elevation change, high to low for body hook (helps establish position). I.E: jab low, jab high, lead hook body..... or jab, lead hook high (slapping hook to get gloves up), lead hook body..... or my personal favorite; feint jab, lead uc (short shot, just to raise up guard, pop up chin), lead hook body. If I really want to get maximum power into the shot, then......jab, feint cross, lead hook body. or jab, rear uc (set up shot), lead hook body.
Find some YT clips of Saul Alvarez, Saul IMO throws one of the best left hooks to the body and is very good at setting it up (particularly behind his rear UC).