Relating (chain of ideas)
This is a fancy term psychologists use to describe when you jump from one topic to another. For example, she might tell you that her neighbor bought a nice car. Then you could ask what kind of car both of you should buy in the hypothetical future. This could easily lead to you discussing where you might live once you are done with long distance relationship or where you wanna travel together during the holidays.
Tell me more
This is kinda close to what psychologists do on TV. Your partner tells you about her/his day and you simply ask them to tell you more about an activity. Even if you do this as a reflex and pick a totally dull activity like laundry. You might still get lucky as some details of her story may be good enough to relate to (hence first technique) and you simply move on.
Pick funny facts throughout the day (Preparation)
It’s very likely that you stumble on plenty of funny videos or interesting stories on Facebook or so. Since you do it anyway, just make it a habit to remember them. This requires minimum effort, but you suddenly have another 30 minutes to fill during your Skype call. You can also go the extra mile and search for some fun stories on purpose. The same goes for videos, pictures, memes, online comics… you name it.
Find new common topics
Even if you use the tips above, in the long run you’ll end up recycling the same ideas over and over again. Your conversations might become monotonous and remember monotony is bad in LDRs. You should look for new common interests, like reading the same book, or following news stories (e.g. presidential election). This will give you plenty to talk about. Add the benefit of personal insights from your discussions and you will be learning a lot. And you know what? Learning new things together is the best way to grow as a couple.
Alternatives to talking
This might seem counter-intuitive at first, but bare with me. Remember how sometimes you just hold hands/sit in quiet when you are together? There is this funny feeling in the air. A mixture of tension and relaxation. You can achieve something similar when you are at a distance. A simple example would be watching the same movie, but not texting during it. You maybe thinking: dude, that’s the opposite of what I wanna do. But once you are done with the movie talk with your partner. Both of you will be bursting with emotions and things to say.