When your bracket has to be at a certain place, the best way to start on sheet rock is to mark your spot, hold the bracket in place & mark through the holes to get exact placement. Insert your screw in the bracket, the bit in the screw head, & use the bracket as a holder/guide for the screw as you drive it in. If you hit wood, great! If not, back the screw out & you have a starter in the wall. If you're using 1/4' mollys, just ream the hole out with a #2 phillips screwdriver & you're ready to go.. Never just hammer a molly in without a starter hole even though a lot are made with a sharp point & small plastic cone on the end. You might hit a stud. You might hit a block wall that has shallow furring strips. You might knock a mushroom hole on the back side of the sheet rock. Then that spot is not just a problem for you. It's a weak spot until the area is patched with a new piece. This is why I like mollys. If you take them out like I described earlier you minimize damage. I'll certainly admit mollys are not always the right fastener, but I hope you start to see my reasons.
Again, more later. Maybe I'll write a book. The whole hollow wall anchor thing goes right out the window when you're hanging something that would be dangerous if it fell or something too expensive to replace.
Oh BTW, do you know why Molly bolts are so named? The inventor originally called them Molly's bolts after his wife.