@Snarp‘s advice is spot on.
Aside from that, the best advice I can give is to make up a couple of checklists until you can do them mentally:
1. Things I need to have in the boat or in the car before we trailer the boat to launch it.
2. Things I need to do prior to launching the boat and using it.
Notice that the lists say “I need to”. The captain can delegate some task responsibility, but he (or she) needs to be sure of these things.
On the checklists would be things like:
life jackets for all
dock lines
fuel (for motorized craft)
working battery (for boats that need electric power)
sailbag and sails (for those boats)
paddle (for all boats where motors and wind can fail, and can be paddled)
anchor and anchor line… anchor line tied securely to anchor
etc.
You’ll want to make your own complete checklists… and then print them and use them.