The site "battery university" has a series of well written articles on how lead-acid cells age, and how to get the best life out of them.
Summary: Avoid deep charge cycles. Keep it fully charged. Avoid long-term overcharging and mechanical abuse.
But getting full charge without over charge is a bit of a tradeoff.
It is simple (cheap) to build a charger that will keep a battery fully charged, if you're willing to accept over charging.
It is more difficult (expensive) to build a charger which keeps a battery fully charged without over charging it at room temperature.
It is really challenging to build a charger which keeps a battery fully charged without over charging it when not near room temperature if the charger does not have a way to measure and compensate for the temperature of the battery.
Since you're likely not going to be using a charger with a temperature probe, you'll have better success if you keep the battery near room temperature. The charger will still not be able to compensate for battery temperature, but a least the assumptions it makes won't be too badly wrong.
Then you can either use a cheap charger and turn it on for a few hours every couple of weeks (which I'd forget to do, of course), or get a fancy one and leave it plugged in.
Worst case would be to leave it hooked to a charger outdoors for months, or to let it fully discharge and sit.