While blisters are probably the most common woe of hiking the trails, don't forget about your ankles! Blisters might be a more common problem, but ankle problems can be much more serious, and much long lasting. If your ankles are already weak and easily injured, you need to do even more to protect them.
First, get good boots!
If you're worried about your ankles or you're going to be on rough trails, make sure you get a pair of hiking boots that provides stability and helps to prevent you from rolling your ankles. Don't get something too heavy, though.
Honestly, some people even opt for running shoes over boots because they don't think boots help with ankle support, but I don't agree with this quite yet!
Now, exercise your ankles!
Most research says that if you want to prevent ankle injuries, you should focus on strengthening and stretching your ankles! So, make sure you do that before and after hiking. Also, don't get really heavy shoes: if you do, your legs will tire quicker and make your footwork clumsier. Both of which will put you at much greater risk of injury!
Here's some exercises: stretch your calf muscles, do some ankle rolls before lacing up your boots, make sure your entire body is loose and limber before tackling a steep section of the trail. When you're lying in bed in the morning, point your toes away from, and back toward, your body. Ah! Feel that glorious stretch? Make it a practice to rotate each ankle in both directions while you're in the shower (just not simultaneously!)
If you have an old ankle injury...
Now, this isn't for everyone, and most people will scoff at it, but if you have troublesome ankles that sprain easily due to an old injury or just general weakness, get a brace! I've never re-injured my ankle when wearing an ankle brace, but without one it happens regularly. And I still recommend that people with healthy ankles wear real boots–over-the-ankle, leather boots–because they’ll help prevent injury.