We each have our own favourite method for opening a stubborn jar lid. The folks at America's Test Kitchen have a great selection of tips that will open any stubborn lid if your preferred way doesn't work.
We've discussed several of these before, from the rubber band method to plastic wrap or hot water. One tip I always seem to forget is to put plastic wrap over the opening to make it easier to dislodge next time. The best thing about these suggestions is that they all work without requiring you to buy a special gadget to do the job.
How to Open a Stubborn Jar Lid [America's Test Kitchen]