One important thing to remember is that you don't have to hit your second target with all steps of your enmity combo before moving on to your next target. Here's what I do. When I can leave the main mob and establish enmity on the other two, I'll throw out step 1 of the combo on the main mob (mob A), step 2 on mob B, and step 3 on mob C. If I need to build enmity on the main mob again, I will do that at this point. Otherwise, when I go to build enmity on the additional mobs again, I'll do step 1 on the main mob (mob A), step 2 on mob C, and step 3 on mob B. Remember that step 2 doesn't build as much enmity as step 3, so I never hit secondary targets with the same step. This equalizes enmity between your additional targets.

Why not just combo them 1-3 in one go before switching to the next mob? This builds enmity on more than one target per combo to prevent mobs from running off quickly, and by the time you've landed your two combos, you have the same amount of enmity between them that you would if you were just single targeting them per combo.