The only thing I did when I gave blood was fill out a form saying that I hadn't taken drugs in the last 2 weeks or so; that I wasn't ill; and that I had never had gay sex. Then they did a blood iron test (finger prick) and that was me ready.
It wasn't sore at all. I don't see why everyone is so scared of needles.
They usually make you wait 4 months before giving blood again but I am not sure if that is how long it takes you to replace it.