What can someone do to prevent nose bleeding?

There are a good number of reasons for nose bleeds. Knowing the reason why a nose bleed is occuring is important so you can prevent it from happening again. If your nose tends to bleed when it is dried out, keep it moisturized and use a saline rinse from time to time. If your nose bleeds when you go to high elevations, a saline rinse or humidfier can help.
Picking your nose is a sure culprit for causing a nose bleed so use a tissue and don't stick your finger up your nostril if possible.

Getting hit in the nose will cause it to bleed so, avoid fights if you can and when goofing around, pay careful attention to your nose. Smoking, frequent use of cold medicines, and getting too overheated can cause your nose to bleed as well so beware of the things your nose is sensitive to and work on awareness. All in all though, nose bleeds are to rid your body of a backflow of blood so blow it out and go with the flow.