For the majority of my friends, we have an ongoing conversation. I'll send a text, then they'll send a text, and it just goes on from there throughout the days. That's not a rule we have or anything. If I wake up and want to talk to them, then I'll send them a text. Usually, I tend to send texts to my offline friends when I think of them throughout the day. So if you're an offline friend of mine and you get a text message from me in the morning, and I was the last to reply the day before, that means I thought of you and want to talk to you.
I've noticed some of my friends are very strict no double texters, so if I don't respond to them, they usually won't text me until they start to miss me or have something important to say, or a question to ask. I kind of think its stupid that they have that etiquette, but it's whatever. I'm usually the person to initiate a conversation with someone, so some days I just decide that I'm going to wait on the other people to talk to me. Sometimes that ends up with me getting, like, one person talking to me throughout the day, and while that's disheartening to me, I also take texting a little more seriously than some of my friends.
Texting is just important to me. I mainly blame the fact that throughout high school, I was predominantly talking to people online. So I developed a need to have written communication with someone when I'm not around them. And if I don't see you that day, or for a few days, then I'll want to text you. Just a casual conversation that goes on whenever we have the chance to respond to each other. Nothing major or overbearing, though when I first start talking to someone, I usually dedicate most of my time to building a relationship with them so I text them much more frequently than I do my friends that have been friends with me for a while.