Hi Karen. I am a now Horticulture student, landscaper/professional gardener, and have worked with my mother's apple trees over the years. Most fruit trees bear in cycles: one year heavy, the next year scant, so a scant year is normal. Pruning will help though.
Also, the best time to prune is in the winter, but I have never done that LOL. Really, if you at least do just a little at a time that should be fine. You want to try to avoid pruning when it is flowering or fruiting, but it won't be that big of a deal. In Autumn after leaf fall through spring before bud is ideal.
-First, just prune off the dead and diseased stuff. That's probably the most important part. If a branch, even a tiny one, is dead and rots, if not pruned off so the tree can heal over that spot, it will literally rot all the way down into the core of the tree, eventually.
-Then another time, the little branches called the water shoots that shoot straight up from the bigger branches. They basically use up the tree's energy so it has less to flower & fruit.
-also, the little sucker shoots at the base the tree, or "root suckers"
-Then, yet another time you can do more shaping and thinning. Proper aeration is important, but more so is pruning branches that cross & touch others. That can also cause disease. Also, ones that grow towards the trunk
It sounds overwhelming when you think of it as one HUGE project, but it is actually better for the tree if you split it up. That gives it time to recover.
Here's also a good website
DEP: Rejuvenating Apple Trees Fact Sheet.
Anyway, if you have questions just ask. It's not terribly complicated once you get out there and figure it out. Don't let it intimidate you. If you want tips on pruning techniques please don't hesitate to ask.