See title.
Could apply to either tabletop gaming or play-by-post.
Could also expand to player burnout?

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Some ideas...

(Tabletop) Alternate with another person, as in you run your game one week, they run their game next week, etc.

(PbP) Don't bite off more than you can chew. Only take on as many players/groups as you can reasonably handle. Resist the urge to just take on as many as possible.

Run campaigns with an end in mind, as opposed to just ongoing. When it ends, it doesn't feel abrupt or unplanned. Then you can pause and refresh, and then run that other idea you've been wanting to run. :-P
You might have an ongoing campaign, but done in chapters/sections.
In between your campaigns, another person might run.

Worst case, take a break, or call it off. If it's not actually fun, it's not worth playing.
You're not obligated to run a game.

Run games you want to run. Sometimes GMs just run games because they haven’t played in a while or because the party wanted to try something and now want to stick with it.
If it’s not your style then there’s no shame in letting someone else GM.

Set a reasonable posting rate for yourself.

Allow players to give you plot hooks.  Look for interesting bits of background, or character traits, that you can use as fodder for a plot idea.

I found having a post schedule very helpful.

No matter what happened in game I was only making GM posts on Tuesdays and Fridays because they were the days I had time to dedicate to sit down and post. (other than OOC missives and such)

If you are posting "whenever I have a sec" you will quickly find that those secs will get filled.

While I don't do gming on PBP anymore, I run two games one online only, the other mixed online and in person. I've found that taking one session off each month helps keep burnout down. I usually take the last Saturday off (game is every Saturday night) unless there is an event that would conflict. This gives everyone the ability to have one weekend a month that they can plan to do things without it conflicting. It also helps me with recharging.

The other game we don't do this but I only have 5 players, and schedules conflict enough that we only get about 80% of our scheduled games due to attendance, so I haven't needed to do this.

This might work in PBP but The pace is slow enough that this might be too disruptive.

Do less work. There are lots of ways to lever back on the amount of effort a game takes, and still run something everyone enjoys.