the need for constant and real communication. With my ex, we talked constantly, but looking back on it it was all rather superficial and we mostly talked about whatever he wanted to talk about. its something that may come up in a regular relationship too, but its amplified so much more when all you have is IM/the phone.
finding ways to show eachother how you feel about eachother when you can't be together This gets a bit more tricky if you take the five love languages into account. Some people need to be shown love in certain ways and you've got to find ways to accommodate that long distance.
Making time to be together regularly in person. You really can only know so much about a person over the phone or online, even if you're both being completely truthful. and there's a completely different dynamic when you're face to face.
LDRs, especially if they're kept up over a long period of time can also be quite costly financially just because of travel costs. phone costs may also add up, but luckily there are programs like Skype and a lot of cell companies offer reduced rates if you're with the same company. and there's also gifts. Just sending Christmas presents to my ex cost me an arm and a leg. I quickly learned the benefit of ordering and shipping online within the US
And I know I already mentioned this, but it is soooo important to come up with a plan at the beginning that you both agree to to end up closer to each other at some point. Its something I honestly wish someone had told me before I started dating my ex. We were long distance for three years and by the end of it I was just so emotionally drained that the thought of ever dating long distance again was enough to depress me.
there are probably other things to think about too that I'm forgetting about. but this gives a general gist of whats involved.