Best Way To Maximize Preamp Tube Life?

I'd never leave any tube equipment on 24/7. Some have standby mode, in which only heaters are lit, some also have soft start circuits, both minimize wear. The rest you're choosing between wear and tear from being used 24/7 or same from inrush current, voltage. So, sort of depends on how often and how long you listen to music. Daily listening, may as well leave on. Still, I don't like leaving tube equipment on unattended, too many bad things can happen. Preamps slightly less worrisome here, still?

I'd never leave any amp on 24/7, regardless of how often listening. I've always thought ss best for multiple daily listening sessions.
I subject the expensive tubes I prefer to the lightest wear possible, they are not simply disposable items to me.  I'm once a week, long term listening session guy.

I have purchased a spare set of tubes for all my components. In the unlikely need to trouble shoot they are there. Also, when the 3,000 hours are up. Sure, they may last longer.

I also have the DS preamp and the 6by5 and its variants are anywhere from 6 to 20 bucks for NOS that should last 8 to 10k hours...at least.  The 6sn7 tube is not in short supply and aren't very expensive for NOS either.  I happen to like the Shuguang Dawning series WE6SN7PLUS tube and have a spare set.  Unfortunately they are out of production but if you get past 50 hours or so on them they should last you thousands of hours......especially in Don's preamp.  Basically, buy a few spares of the 6by5 and a spare set of the 6sn7 and you'll be good to go for many years assuming you get a reliable set.
No 24 hours on.  No waiting an hour or two for warm up.

Speaking of testers, can someone recommend a simple, cheap unit that I can use at home?  Just recently got several tube units (Schiit pre, Decware amp) and have a bunch of tubes from prior systems.

You should probably leave your space heater on 24/7 too.