When I went, they wouldn't let me do it because I was on a certain medication. There are many things that disqualify you from selling plasma apparently. Your blood pressure and iron levels need to be normal, you can't be taking any medications or have any illnesses (well, some illnesses might be fine, but I would still lie just in case), you can't have any family history of illnesses either, you have to practice safe sex, not have done any kind of drugs or shared needles before (I would also lie about your history of alcohol addiction), and I think you even need to be under a certain weight limit if I recall correctly...or maybe it's BMI, I'm not sure. But under like 300lb should be fine. Oh, and I don't remember if they want you to eat or not prior to the procedure, but I wouldn't just in case, and if they do want you to eat, they'll probably give you crackers or something.