Blisters are the result of moisture building up between the layers of skin on your feet. This moisture builds up as a result of friction and can be exacerbated by excessive moisture inside your boot. Your feet release a tremendous amount of moisture. To the point it's gross. To reduce blisters, you have to combat moisture inside your boot in general and mitigate the friction in problem spots.
As mentioned above, socks are the key. People seldom realize the importance of a good sock. It goes way beyond the type of fiber used in the sock, but how it's used. Obviously, cotton is evil and should never be let outside your house...ever. Cotton is just terrible. Wool (Merino) and some synthetics are the way to go, but don't just buy based on material alone. A Smartwool Phd sock for example is woven in such a way as to control the collection and transfer of moisture. In a nutshell, it takes moisture from the bottom of your foot where it is most heavy, and draws it out of your boot to the cuff of the sock where the moisture evaporates, kind of like a little radiator/evaporator. That particular sock even has a thinner "window" woven above your toes so moisture can radiate through your piggies to the top of the sock. In addition to this, the sock (any good sock) adds important cushion and additional volume to the shape of your foot to optimize fit to reduce the chance of slipping - friction. I'll take crap boots and a good sock over $500 boots and a junk sock any day.
Socks are usually the best way to mitigate blisters, but it's not the only way. Since this is often about moisture, sometimes taking off your boots and letting your feet dry helps. I have used alcohol pads to wipe my feet clean and expedite the drying process. Toss on some dry socks and away you go. If you have friction you can't mitigate, that needs to be addressed the exact instant you feel a hint of a hot spot. Re-lace your boots, change your socks or cover that area with one of the many blister aids available asap.
And sock liners are not as necessary now as they were years ago when sock weaving technology was less sophisticated. Bite the bullet and buy Smartwool Phd socks. They'll run nearly $20, but they do the job of 4 pairs. I can often backpack for 3 days on one pair.
You might also be able to improve the fit of the boot with an improved insole. I'm an advocate of Superfeet insoles. The crummy $2 insole in most shoes is pretty lame. People often wax poetic about the fit of a boot, but seldom mention the footbed. People love to toss around the term, "arch support" but most boots by design don't have much contour on the footbed. And arches don't get supported under the arch. You support a foot from the heal first as that's where all of your weight is. Insoles like Superfeet not only add more contour to a boot where it's needed most, it helps all sorts of fit and efficiency issues.
Dang this is nerdy stuff.
Hope that helps.
