#1 - some topical - whether it actually works or has more of a psychological positive benefit is debatable. I use it for all of my injections though. I'll place my cotton tip applicator with topical on it, joke with the patient about it's taste for a moment, and then go wash my hands and glove up, so the topical is in their mouth for about 2 minutes
#2 - Use a 30 gauge needle whenever possible - the smaller the diameter of the needle, the less resistance it has, the more comfortable the patient will be
#3 - warm the anesthetic carpule up to above room temperature. The temperature contrast between your 98.6 degree patient and say your 72 degree anesthesia that's been sitting at room temperature can cause extra sensory responses upon the start of the injection
#4 - shake their lip/cheek/ whatever soft tissue part is near the injection site. This will help distract them, from what's going on at the injection site. And continue shaking through about 1/2 of the carpule being injected, and then start back up with the lip/cheek shaking just prior to finishing your injection and removing the needle
#5 - DEPOSIT THE ANESTHETIC
SLOWLY!!!! It's not a race. Think about it, you're trying to get 1.7cc of solutuon that is acidic in nature into a space that is alkaline and doesn't have enough room typically for 1.7cc of solution. The slower you go (and I'll typically take at least 30 seconds, if not longer for a full carpule) the more the anesthetic that was initially deposited has had a chance to start working locally to lessen the discomfort as the tissues around the injection site are "stretched" as the 2nd half of the carpule is deposited. Comfort is key! And the running joke about this is "What's the difference between and oral surgeons injection technique and a GP's injection technique? ...... About 30 seconds!"
#6 - Just be confident! And this comes with experience. If you walk into the operatory and start off telling the patient that it won't be a big deal right from the get go, that plays a roll in their perception of how "comfortable" the injection is. Or if I have a patient ask me prior to the injection if it will hurt, my standard, quick, tongue and cheek answer is either "Do you want it to?" or "Not me!"
It's just a little tension breaker I've found that works quite well as you help psychologically manage your patient through the injection process