For a blister preventative, try this – polyester dress socks as a liner sock. Your climbing pals will envy you as the best dressed hiker at the trailhead, and your feet will be happy as the slick synthetic socks slide right over those problem areas of your heel. Blisters are typically caused by friction, and if you can minimize friction inside your boots, you decrease the chances of a blister forming.
I once had some boots that took a long time to break in, and I had constant blister problems. After trying most other blister preventative tricks out there, I gave this as try – even though it sounded pretty goofy. Not a single blister.
You can buy low-end dress socks for about 3 pairs for $10. Costco usually has multi-packs for a super low price.
It's fine to combine this with preventatively taping your known problem areas, such as the back of your heel. Remember to use tincture of benzoin on your skin before you put on the tape, to make sure the tape doesn't slide off.