Draining the bottom to empty eventual accumulation of sludge on an annual basis - and replacing the sacrificial anode (that is supposed to corrode, not your tank) as needed. "As needed' depends on your water. Can be anything from every two years to once every ten years.

The sacrificial anode is $15-$20 in most cases and relatively easy to inspect and to replace. In my case even with limited headroom above the tank, managed to pull out the old - not badly corroded one - and insert a new one. No need to empty tank, just drain it a tiny bit to ensure water does not leak out the top when anode is removed.

Still, I think that is a task that 99.99% of users never undertake, as we are taught that hot water tanks are 'install and forget' and only 'should' last 5-10 years.

I do inspect burner if via the opening, try to ensure no dust has accumulated underneath (have pets, dust occurs on basement floor). I try to keep tank clean and dust free on the outside, make sure flue and vent hood are properly connected and in good shape, etc. Same goes for the china cap and B-vent exposed to the outside elements.