What should an aspiring writer work on?
Doing the stuff you intend to make your characters do. Seriously, people, please do all the impressionable minds out there a favor and actually do your homework on this.
(Can't experiment with time travel? Okay, I'll give you that one.)
But have you ever walked anywhere in your life? If you're planning on writing a book with any amount of walking, (and I'm looking at you, fantasy authors) pick a destination and walk to it. Take notes: speed, feels, actually arriving somewhere.
Then walk BACK: yeah, that return trip can be a killer. Now you know how walking feels, and can write appropriately.
This should be "required doing" for all books that involve characters walking places. I'm in a book right now, where the characters walk and walk, bypassing domesticated animals wandering around after a tragedy. WHAT???
Grab those critters and ride, folks! Come on! I call foul. (Oh, and most of the characters are wounded.) That sound you heard? Yep. Me internally screaming.