All of the reasonably simple solutions are compromises, and all of the ideal solutions are circuit dependent. They also depend on what you want from them - longer tube life, better sound sooner, reduced turn-on and turn-off thumps, etc.
For example, the "soft-start" board in Paramount delays and slowly applies plate current to the driver tube. This helps protect the 2A3 if it is configured for the direct coupled 2A3 circuit, by keeping the grid near ground. It does not prevent high voltage on the output tube before the cathode warms up, so the longevity could be even greater. Amps which are not direct coupled will see little advantage, and it won't survive unless the voltage is limited at startup - which the Zener bypass on the shunt regulator provides, until the shunt reg tube warms up and takes over. Other amps that do not use C4S plate loads on the driver can't use it, and without regulation they may even destroy it.
For another example, again Paramount, ideally the output transformer would be shorted across the primary until the tubes are warm and the voltages stable; this would prevent the start-up transient from magnetizing the core. If you have nickel core transformers, this eliminates the 1-hour warmup with music needed to de-magnetize the transformer for optimal performance. This is only applicable to parafeed outputs, and mostly just to nickel core transformers.
The most common approach for most circuits is to delay and slowly ramp up the high voltage. Switches and time delay relays can delay the voltage and eliminate initial over-voltage, but not slow the rise. Slow-warmup tube rectifiers can do both, but the rectifier warmup must be slower than the slowest tube, and the rectifier itself is not protected.
In the case of switches and relays, there are no affordable switches that are rated for more than 240vAC. (DC ratings are much less and only AC should be switched.) Switches are widely used beyond their ratings, but of course in that case are less than reliable and potentially dangerous. (Paramount, again as the example I am most familiar with, has a 200v winding with voltage doubler, so it can be switched.)
The cleverest simple scheme I know requires separate transformers for heater and high voltage power. A pair of double-pole switches are wired in parallel for the heater power, and series for the high voltage. This way you can throw either switch and get the heaters going, then throw the other switch to start the high voltage power.
