It can be fun to send erotic writing or pictures to someone you are sexually involved with, titillating each other in a low key way when you’re not together.
In regards to writing: a fun way to tease is to say too bad you’re not there or she’s not here or you’d do this or that to her. Keep it to vivid descriptions of foreplay, various physical stimulation. Dominance is also good if you two do that. A fun thing is if she’s telling you she was somewhere, say a theater, then write about getting it on in that theater, vividly in the exact location.
You can also write about being hard thinking about this or that, or remembering last night, etc.. Also it’s fun to tell her to do various things to herself, suck her fingers, touch her pussy a certain way, etc.
Pictures: if she’s into dominance you can’t go wrong with angle up, shirtless looking down menacingly holding a whip etc.
Doing some exercise, or even at the gym.
Some people are into dick pics, personally, unless explicitly requested, I go with, if I want to make a certain point on that theme: get hard and wear clothes on top of the cock, so the portruding shape is clearly visible, but much is still left to the imagination.