It would depend how well you know them and what the prior relationship, if any is. Regardless communication skills and honesty would be essential for both parties. You should also give consideration to the following.
1) How often will you contact each other, who will contact who, over what medium, etc. Try to keep it realistic, while one of you calling the other every day might be sweet in your mind, it might be overbearing for them (or vice versa).
2) Issues of monogomy. You don't see each other, in many cases there will be temptations. Are you both willing to be monogomous? If neither of you wishes to be, what sort of "allowances" are granted?
3) Is there a long term plan? Do you plan to live in the same city at some point and be a "normal" couple then? What do you ultimately want out of this relationship, and is the distance factor worth fighting against to obtain that with this person?
For some people and couples, LDR seems to work perfectly. For others like myself, we can't even really imagine it except in cases of utmost necessity. The key elements I've heard from others all seem to revolve around making absolutely sure you both have the same expectations and are willing to adhere to them (not merely pay lip service).
