Back up everything
If you have ever deleted anything accidentally, or suffered a computer crash, you will probably not need to be told about this. Back everything up at least once a day. I use Carbonite, which automatically backs up my whole system every day at 6pm. So, if I lose something or my system dies, I have a copy of everything easily accessible online.
Bookkeeping and invoicing
I would recommend allowing time, twice a month, about two weeks apart, to pay all your bills, input all your expenses, raise all your invoices and check that payments have been made.