Ugh I wish there was a single answer to this.
To be honest there are many ways to motivate yourself to draw:
-accepting that it will always be hard to start drawing, no matter how experienced you are. You just have to jump in, and struggle until you start getting hang of it, eventually (or not lol, sometimes struggle is a an hour, sometimes its a month).
-realizing that drawing is 50% hand/eye coordination and 50% your brain knowledge. Its essential to read into your subject matter, study it, books, wikipedia. If you want to learn how to draw dogs, read wikipedia about canines, study their evolution, species, how they differ, physiology, facts. An image is more valuable than a thousand words, so make sure you know your thousands before you try to make that image.
-Draw what you hate, never stay in comfort
-Draw whatever comes to your mind
-Draw from real life as much as you can, its 100x better to practice drawing people by going outside rather than from pictures.
-Critique yourself. Make mistakes, look back, point them out and write them down next to your drawing. This is very important. If you can’t critique yourself that means that you don’t understand what’s right or what’s wrong. This is same thing as mindless doodle. Again, make mistakes, when I draw something, I draw it 10 times, even if first time it looks alright, I’ll change the angle, I’ll improve a certain part of that object. Its all about producing large quantity of stuff.
-zero expectations. This is important if you don’t draw a lot. Because every line you make is loaded with expectation of being good. That can handicap your looseness and prevent happy accidents from happening.
-Challenge yourself. Compete with yourself.
-Always carry your sketchbook everywhere you go. You must be able to get it out and start drawing in less than 30 seconds (I just have it in my hand all the time and some pens in pocket). No excuses, you can draw anywhere, anytime.
-Go outside to draw. Sit in the park, go ta a cafe. Get some nice music/podcast and go out and draw for yours soul pleasure
-Keep distractions to a minimum: Video games, youtube, social media, internet, messaging. Remove them, learn to say no to those things if you really want to draw more
Well I’ll stop now, this post is already too long.
but hey, I hope this kinda answered your question :D
Good luck with your arts!