You must be in good health for donating blood and good health means you have no fever and feeling well on the day of donation. You must have a good meal al least 3-4 hours of donation. Check your body temperature before donation. If you have a body temperature 100 degrees Fahrenheit, you must wait for overcome until fever is no more. . Final eligibility is determined by medical professionals at the time of donation.
Everyone can donate blood but there are some donor eligibility criteria which may very for some countries or blood centers. But general criteria remain the same for everyone.