I think that anyone who can be a surrogate is a very selfless person. If you are serious about doing this then you need to do lots of research, and need to think it through very hard because it is not something that you can go into lightly. Things you need to think about are:
having to go through pregnancy, and all that that entails, including possible complications, giving birth to a baby and then having to hand it over to its new parents.
another couple essentially becoming a part of your life, coming with you to scans,anti natal appointments, and even the birth.
the possibility of the relationship with your baby's new parents breaking down either during or after the pregnancy, and you still having to hand your baby over to them despite your potential feelings towards them.
being judged by people who findo ut what you are doing, eg friends/family/members of the medical profession. Not everyone considers surrogacy to be a wonderful, selfless and noble thing, and you will be judged by those who simply will not be able to understand how you can carry a baby and then give it away.
how your partner and other children will feel about things. Some men find it very hard to deal with the thought of their wife essentially carrying another man's child. Also how will you tell your children that you are having another baby but that it won't be their sibling. if you have artificial insemination, so essentially the baby will biologically be yours, are you prepared to tell your children that they have a biological sibling but that you have given him/her to someone else? also, how do you feel about a biological child of yours being brought up by someone whose parenting methods are not necessarily the same as yours?
if you become a host surrogate, you will have to have IVF, this is invasive and there are no guarantees, do you have the time/emotional strength to go through these treatments?
Sorry if this paints a very bleak picture, but these are all things that need to be seriously considered IMO. I couldn't be a surrogate, not even for my own sister/best friend.