Epistaxis can occur accidentally, especially among children and elderly, either in summer (due to high temperature which causes engorgement of the nasal plexus) or in winter (due to dry air which irritates blood vessels in the nasal plexus). 
Epistaxis itself isn't a medical condition, it develops as a warning signs for many health problems; the most common causes of epistaxis include the following:
•    Hereditary hemorrhagic telangiectasia.
•    Direct trauma to the nose or the face.
•    Nasal polyp or deviated nasal septum.
•    Allergic rhinitis.
•    Marked elevation of blood pressure.
•    Coagulation disorders and bleeding tendency.
If epistaxis occurs, it's advised to do the following:
    Lean your trunk forwards (don't tilt your head backwards as most people think).
    Use your thumb and index finger to apply gentle pressure over the fleshy part of the nose for 5 – 10 minutes.
    Over-the-counter nasal decongestant spray can be used.
    If epistaxis continues, you should seek urgent medical care.
On the other side, to prevent epistaxis, it's advised to do the following tips:
1.    Proper management of medical problems that may cause epistaxis, such as; hypertension, deviated nasal septum, nasal polyp… etc.
2.    Use air humidifier: this is because dry air triggers epistaxis.
3.    Use over-the-counter saline spray: so as to keep your nose moist.