There are many types of hemorrhages that you can see in the retina. There are microaneurysms and dot-blot hemorrhages (from diabetes), flame hemorrhages (from hypertension), mid-peripheral hemorrhages (from carotid disease), diffuse hemorrhages (from vein occlusion), sea-fan hemorrhages (from sickle cell), or subretinal hemorrhages (from macular degeneration).
Most hemorrhages from diabetes, hypertension, carotid disease, and vein occlusion will resolve on their own (provided that the underlying disease is controlled). But sometimes, they can take a long time; and we have to help it with some laser treatments or injections. The hemorrhages from sickle cell and macular degeneration usually needs treatment right away. If your eye doctor is uncertain, it would be a good idea to see the retina specialist.
The other part of your question about prevention depends on the underlying problem. I agree with check the blood sugar, blood pressure, lipid profile (cholesterol). I would also check a carotid ultrasound (to look for clots and plaques in your neck). The type of hemorrhage can also guide the hunt for the cause.
I hope this helps and thank you.