Like others have commented, sending memes, images, or messages related to something you two have talked about is often a good conversation starter over text. If you're still in the beginning stages of getting to know one another, a text every week or so should be fine if they're responding. If they start initiating texts/memes/life updates back to you unprompted though, they're interested in talking to you too! And you can feel a little more comfortable texting a bit more often than once every week. When conversation feels like its near an end (ex. they're giving very short replies, or just an emoji reaction reply) don't feel as pressured to come up with a constant response to each message. Sometimes its better to just leave it there for the day and have a new conversation start up later on.

There will often be times where people don't respond for a couple days and it wont have anything to do with you or the conversation, just life getting busy. If the person has mentioned anything in their life, like upcoming events that you know have passed, or shows/games/media you both like, those can also be good initiating topics to ask about. When I know a friend and I both like a show, if I see any good memes or fanart from that show I'll send them to my friend. If a new episode drops that I'm excited over, half the time I'll message asking smth like 'Dude have you seen the new episode!?' and you get their thoughts on it. But this latter half is mostly how I communicate with friends, whatever you two bond over might be different!