Helpful tips straight from me to you.
Don't be that person who replies "Sorry, Dan who?" when your friend brings up their new co-worker they've mentioned three times before. Making the effort to remember names and details of the people your mates mention means they'll feel more comfortable talking about them and keeping you up to date with what's actually going on in their day-to-day lives — which might have a lot to do with their colleague's totally undeserved promotion.
I have a lot of thoughts about chronic cancellers, the most important of which is that they're the hardest people to maintain long-distance friendships with. I'm totally guilty of cancelling calls at times, but am trying to be better. When you live apart, there might only be a few times a week or month that you're both actually free to talk — and if one person cancels, then another, before you know it, you haven't spoken properly for a couple of months.
Even the best of friends can drift apart. When you're no longer nearby there's no running into each other, or new restaurants to try together, or "I'm going to be in your suburb tomorrow, will you be around?" Just as couples in long-distance relationships work hard to maintain closeness and show their affection, friends need to do the same. It can be done — I promise — but you both need to work for the friendship that's worth it.