Drain thoroughly. This may mean drain and partially refill and then drain again. Or just drain, and leave the hose running for awhile with the drain valve open. Whatever works for your tub to get as much of the old water out as you can.
Flush the plumbing lines. This may mean simply putting the garden hose in a couple of jets, or it may mean drain, refilling, running the jets, then draining again. Again, whatever works for your spa to get as much of the old water out as you can.
Wash the filters by soaking in a non-baqua filter cleaner. You most likely needed to do this anyway.
Refill, balance, and shock with Dichlor.
Heat, and add people.
