You see this in a lot of business type books and resources. "Pay yourself first" usually means something like waiting until the last moment to pay back debt (or make a payment on one) or some other form of valuing yourself over others.
But you can apply it to other aspects of life, and without needing to appear selfish.
You can get a workout in first thing in the morning. That way, you can't say "I'm too exhausted" at the end of the day.
You can get your practice in before you sit down for your "day job". Again, you can't say "I'm too tired now" because you already paid yourself in getting your practice in.
Try it for a while. Write your blog post; practice music for half an hour; indulge in a full hour long workout. No problem. Because you made the time for it and that time is "before I pay my time to anyone else".
Bonus points for morning people - you get the best version of you when you do it first thing in the day.