Blisters normally form from some sort of abnormal motion when you're walking. It could be how your foot rubs against a shoe or it may be the way you're walking. Identify what's causing the blister to form and change your shoes or walking motion. If the blister is just irritated skin, leave it alone and it will eventually dry out fine. You may have to put some sort of bandage on it just to protect it from being painful. If the area has fluid in it, that's when it gets a little bit more tricky. You'd have to make sure it's very clean and wash the area. You may actually have to drain it a little bit if it's a big area with fluid and you might have to do that with a sterilized needle, just to get the fluid out. Then, bandage the area and let it dry out on its own.