Can you do anything to make power tubes last longer ?

Be sure you know what you are doing in setting bias on the low side.  If the measurement is in mA, the lower number means running the tube more gently.  If the bias is in mV, a higher number means lower current and gentler treatment of the tubes.

Thanks for that, @larryi ; I was not aware.  I had read some stuff on bias before that had me confused.  However, my amp is biased using mA and I do run it a bit low.  

I would THINK (and I may be wrong) that if the suggested bias parameter is given as a value between settings, setting to the lower end might be healthier for the tubes. In other words, as an example, if the suggested bias was given as something like 240 mA to 300 mA going towards the 240 mA end of the deal might be easier on the tubes. But I do not know that for sure.

Also to make sure that they have plenty of ventilation.  I suppose one could even set up a small fan.

And if there is a sequence to 'soft start' them for your amp, to always adhere to that.

And fewer on/off cycles, I suppose ?

I think that there may be differing opinions on that, @inna . Personally, I do not like to leave output tubes idling when I am not around/in the close by vicinity. The older I get the more neurotic I get.

But the way I listen these days in only once or twice a day . . . it’s ot like I am in and out and turning music on & off. I will say, however, that even back in those days I never left tubes on when I was out of the house.

But: the sort of exception was with my first tube amp before I knew anything at all of what I was doing. It was (and I still own it) a Cary SLA 70 signature and it has a standby switch. With the standby switch in ’on’ the tube filaments are constantly being heated. I’d have to get into the manual to tell you exactly which filaments are heated and glowing, as tubes and electricity is not second nature to me. Anyway, as I was learning the hard way basic stuff that every tube owner should know, I was talking to the service rep guy from Cary (this is back in the ’90s when they had great customer service) and he said it was not his advice to always leave the amp in stand by as I had been doing. Therefore, I then started using the standby switch in sort of a sequence . . . in other words first go to standby for a while before I went to ’ON.’

As far as preamp tubes, I don’t leave my pre on when I am not listening, either, but there have been threads on that subject, and I know that there are some that do.

  I have always been told turning amps on for short periods then off is bad for tubes. 

I would think that repetition would be the key to avoid on this one.  

Good tube equipment will last for decades with only occasional tube replacements.

Hmmm . . . decades?  I don't think you will get decades out of output tubes unless you skip using your amp for a decade or so.