Best way to prevent fainting?

I know that fainting is caused from many things, but especially from the drop in blood pressure and heart rate from the vagus nerve causing a lower supply of oxygen to the brain. fainting is a way to get your heart on the same level with your brain, basically to get you to lye down,
but does this mean that if the oxygen supply was brought up enough fast enough fainting could be prevented? what should i do to prevent it, please help. (besides medications)

Try the knees between you head already suggested when you feel dizzy. Also, rise slowly from a seated or reclining position. If laying down, sit up first and dangle your legs to the floor for a while. Then slowly rise.
Have you seen a doctor about this?

When you start to feel dizzy, sit down and put your head between your legs and breathe in and out.

keep your blood sugar stable and eat every couple hours

I got fainting spells when I was pregnant with my first child. I could prevent myself from fainting by immersing my wrists in cool water.

Good luck with that.

lie down on the floor and put your feet up on a chair

Go to the Doctor if you have not..Fainting can be a serious thing.
I have that problem some and was told by my Doctor to put your head between your knees.This has helped me.Of course you are in a sitting position when you try this,Thank You.