Even if it’s just a silly doodle or a completely rubbish piece of writing, save it!
This may be more applicable in some situations, but it’s good advice to keep in mind in general. Whenever you practice a skill with which you produce a result, like a drawing, some text, music or anything else really, try to record/store it somewhere for future reference. Not because it’s particularly good, and you likely won’t be taking a second look at it anytime soon. Still, you’ll have recorded the current state of your skill.
And if you’re working on improving, that’s really important. You want to be able to go back and see how far you’ve come. You can’t do that if all you have is your memory of the thing you created! Sure, you can recall what you thought of it at the time, but that’s no substitute for looking at it with your current, broader array of knowledge on a particular subject. When you’re a novice, minor accomplishments can seem grand, and sometimes you’re just blind to the flaws in your work. There’s nothing wrong with that, but if you can look back at it and say “I made that mistake. Am I still doing that?” or “That’s something I learned not to do!” then you’ve learned from your past mistakes and proven to yourself that yes, you are definitely still moving forward.
Granted, looking back at really old stuff can be cringe-worthy, but that’s also part of the process.