Dig out a plantera arena in the jungle so you don't have to deal with hardmode enemies while you do so.
If you want to speed up early hardmode, setting this up is a must
https://m.youtube.com/watch?v=gpYn1xGQXEw
If you need to build anything in the sky, do it now so you don't have to deal with wyrms.
If you want to go fishing anywhere, go ahead and set up your fishing huts so you don't have to deal with hardmode enemies while you build the huts.
Buy some purification powder from the Dryad, this way if you come across the tortured soul in the underworld you can turn it into the tax collector. If you leave to buy powder after seeing one, it will despawn unless you throw coins at it(enemies holding coins can't despawn), and you'll have to wait for him to respawn.
Fortify your shimmer pool and have easy access to it so you don't have to deal with invisible archers.