Finding a good assistant is rough, it requires patience, initiative & chemistry. Once you find 'the one' reward them, because a good assistant is like having a 3rd hemisphere to your own brain -- it sucks when you lose it.
Retooling for an assistant is the most important thing you will ever do for your company, it is what will ultimately allow you to perhaps grow or exit someday.
For new assistants - start them writing down your processes as an operations manual. Every day, they should be making updates and journal entries in the operations manual. The primary purpose of this is to see they can write in a way you can understand, if they can't do this - then fast fire.
If you find somebody who can write/edit/update -- Make sure they know "this role temporary, until it is permanent" and their role is to make themselves indispensable by anticipating your needs.
review your inbox, edit your documents, organize your calendar, and do research, follow up with clients, billing/collections, whatever tasks they can identify and offload from you.
A good assistant once fully trained will be 80% right, 20% wrong, .. you need to accept they aren't you - but eventually you'll both find how to make sure they do the 80% .. and defer/check with you for the other 80%.
A good assistant will write things down for your next assistant.
We call this the "BUS" (or Tram) factor.
I know this seems cold & harsh, but having/updating an operations manual should be the first week of any new person as they are training.