To avoid getting nausea the donor must consume lots of fluids along with a healthy food item like a regular meal before donating blood.
They should refrain from taking hot shower or staying in too hot surroundings.
They should refrain from vigorous activity like exercise and should refrain from keep standing for long duration.
Rest well on the night prior to donating blood.
If you still feel like fainting, just lie down for some time and let the blood flow to reach the brain.
Eat more iron-rich foods once you donate blood to recover fast.