Having never actually owned or used one (even after doing a fair bit of camping in grizzly country) I can only take a few suggestions that I have read to heart and add a few logical ideas of my own.
1. Get the big size. It lasts longer therefore a more potent dose. If you don't use it all the first time around, the bear could possibly come back a second time after bluffing you. But it comes in a 10-lb extinguisher, you may want to pass on carrying
that much weight!!!
I'll let somebody else comment on the type of spray and level of Caspian active ingredients.
3. Get the holster and wear it within easy access. A bear spray sitting in your pack does you no good upon a chance encounter!
4. Get the one that has the farthest range and produces a large fog cloud that the bear will have to charge through to get to you. A cannister with a stream spray will be nearly impossible to hit on target especially when you are excited.
5. If you can, get a cannister to practise with before relying on it for your life. Don't wait for the bear to get too close, they can be very fast and be upon you in a second while it also takes a second or two for the fog cloud to build and provide an effective barrier!
6. Don't just stand there in the open! Find a tree to get behind to provide an additional obstacle for the bear to get around! Use a stick, branch or hiking staff or rocks as an additional weapon. Wave your arms, make yourself look big, make lots of noise and generally look threatening! The bear is likely more afraid of you than you are of it; give him a chance to back safely out of the situation too!
7. Of course, if you are facing a cougar, wolf, dog or angry moose the challenges and response are going to be slightly different.
8. This probably goes without saying but you should also try to manoeuvre yourself so that you are UPWIND of the spray and the pepper spray doesn't immobilize YOU instead of the attacking bear!
Does anybody actually think about this in the event of a bear encounter? Maybe, maybe not -- maybe you "fill your pants" before you can get your thoughts together! Everyone reacts differently. All the better to prepare and remind yourself as you pack up and hit the trail-head so that it is fresh in your mind about how to react. Discuss the actions with your partner(s) so that they can remember to "take cover behind the cannister guy" and not become collateral victims of the spray!!!
9. Lastly, pay attention to various local laws regarding the use, transportation and disposal of the cannisters. For example: don't try to bring them across the border into Canada, they will be confiscated. You can buy them here. If not used during your trip you may be able to sell them to another hiker on the trail head otherwise dispose of the cannister in a legal manner.