Up to this year it's always up to the local farmers for my boys - this year helping with lambing and have had plenty of practice - under supervision first till I was okay on my own - think you have go get you own technique but mine is similar to above.
I kneel, lambs front legs over left arm, my left fingers at base of scrotum pushing in slightly and I try to put my finger tips on the nipple so they don't get trapped, applicator in right hand, over and down to my left hand finger tips, release pressure, check all is in place, use left hand to flip ring off applicator and job done.
I have had the odd one I found impossible and asked the Farmer expert to do and so far he's always said they have not dropped yet so I'm. Thinking if something doesn't feel right then it's not right - good luck