There are several methods of healing blood blisters.
For immediate care leave the blister alone and apply a ice to the area. The cold reduces the inflammatory response. It is also advised to try not to let the blood blister come into contact with food, but depending on where exactly the blister is depends if this is possible or not.
In some cases, it is advisable to visit a doctor to ensure that the blood blister is not a symptom of a more dangerous condition.
Refrain from irritating the affected area. If necessary, apply some sort of mouth ulcer medicine as this will help to protect the area from food especially sugar and salt which can cause pain if are able to get to the affect area.
If the blister breaks, quickly rinse out your mouth with cold clean water and avoid eating or drinking anything, other than water for a short period of time to allow your body to seal up the wound
Small blood blisters, such as obtained when something pinches the tongue, may hurt for a minute but soon subside, leaving only a painless blister. Such blisters should be left to heal naturally; there is a possibility of infection if they are punctured, and unless it is painful, the risk is likely not worth it.