They peel easier if you keep them in the fridge for a few days after boiling. Over time, water exudes from the white, forcing the white to shrink, and the membrane to separate from it.
I also add a teaspoon of baking soda to the boil water and that seems to help. I have no theory for why that works but it seems to make the whites a bit more slippery and easier to peel.
Yeah, and to be clear, this is for store-bought jars like pickle jars, not so much Ball jars of home canned stuff. Those are too difficult to get a butterknife into, as they’re pretty flush against the glass. The stuff like jam and such, I like to put the butterknife underneath one of the “tabs” – the are where the lid is kind of folded over on itself – there’s about 6 of them on a jar, and twist. Once you hear a pffft you should be good to go. It does work on the areas in between those tabs, but I like starting there. Usually it just takes one twist, but sometimes I have to go to the opposite side of the jar and do a quick twist there.
I also tap the lid with the blunt edge of a butter knife. Strike it in the direction to open helps. My Wife just gives the jars to me. That hack usually works for her.
If you can wedge it under there, I find a spoon to work much easier since it won’t flex. But, at least for me, I usually have the best luck with my silicone (and grippy) oven mitt.
One of those “church key” can openers works great for popping the vacuum. That’s the can opener with a sharp end for puncturing the top of a can. The sharp end bends up at an angle and provides the perfect leverage to move the lid out just a bit.
Unrelated but I always tell everyone to keep one of those cheap 6 way screwdrivers in their kitchen junk drawer. You’re a lot more likely to fix something (or fix it without resorting to a butter knife) if you don’t have to go down to your basement or out to the garage to get a screwdriver. And that goes triple if you’re going to ask me to fix something every time I’m at your house. Happy to do it, just leave a screwdriver nearby for me.