There are lots of reasons to donate blood: Maybe you know someone who needs a transfusion, maybe you were asked to give blood by a friend, or maybe you're responding when tragedy strikes. Whatever your reason may be, giving blood is important — having a healthy blood supply ready for transfusion to patients who need it is key to saving lives, and so by giving blood, you are giving the gift of life to as many as three people, according to the Mayo Clinic. What should you, as the donor, know for a successful donation? Here are some tips:

1. Who can donate?

First, know if you’re even eligible for donation. The most basic requirements are that donors must be healthy, at least 17 years old in most states, and weigh at least 110 pounds. When you go to give blood, they’ll give you a mini-physical where they’ll check your pulse, blood pressure, hemoglobin level and temperature. They’ll also ask you a few basic questions about your health and lifestyle. In some cases, the answers you give could disqualify you from donating blood. Be sure to check the Red Cross’ guidelines before you go.

2. Before donating, eat and drink this

If you are indeed eligible and plan on donating blood, be sure to eat a healthy meal the night before (if you’re donating first thing in the morning) or immediately before donating (if you’re donating later in the day). Try to avoid very fatty foods (like French fries or ice cream) since that will make your blood too fatty and difficult to test for infectious diseases. If this is the case, your blood won’t be used for transfusion. Also, make sure to drink at least 16 ounces of fluid before you donate, and wear clothing with sleeves that can easily be rolled up above the elbow.

3. After donating, eat and drink this

When you're done, it’s important to drink water again to replenish your system, and to rest for a bit. Most blood donation centers will not allow you to get up right away anyway, so use the time to drink, drink, drink. For the rest of the day after you donate blood, make sure to eat well, including foods rich in iron, and drink plenty of fluids (but back off the alcohol).

4. Take it easy

Be sure not to do too strenuous of an activity, like rigorous exercise or heavy lifting (i.e. don’t head to the gym or help your friend move boxes out of her old apartment) on the day you've given blood. If you start to feel faint or dizzy, stop what you’re doing and rest until you feel better. If you still don’t feel well after a day or start to get sick or develop a fever, seek medical attention.

5. How soon before you can donate again?

Because it takes eight weeks for the red cells in your blood to replenish themselves after donating blood, you have to wait at least that long between donations. If you’re donating plasma, on the other hand (which is collected through a machine that separates your blood components to take only the plasma and then returns the red blood cells to you), then you can donate more often.

While we’re on the topic — there’s another important blood-related substance you can donate — bone marrow. Thousands of blood cancer patients rely on a transfusion of bone marrow from a genetic match. You can easily join the bone marrow registry by swabbing the inside of your cheek with a kit you get online or at a donor drive.