First Timer, i would suggest Calves, Traps, and Lats.
J/k
Go with Glutes, quads, and Delts. You have two cheeks per week, about 3 spot per quad, and until you get the hang of other spots, two delts to inject into. I say this because from time to time, I inject in my front and rear delts, but you have to be handy with the pin and plunger.