A tip I have is that I've always lived by the rule of charging my phone while it's off, unless I'm in a pinch. Heat is a notorious enemy of a battery's lifespan, and charging the phone while it's on (or worse, while using it) will increase the heat more than anything. Doing that constantly subjects the battery to unnecessary stress and will wear the cells out faster.
To back up that claim, my 2.5 year old Turbo still gets me at least 5.5 hours of SOT (it used to be 6.5) and a full day of use. While my wife's DT, which she rarely ever turned off, was barely making it through a full workday without sinking into the teens of remaining battery life.
My battery life has fallen off a bit, especially over the last month, but is still on par with most of the new phones released this year.
The conclusion is that there are ways to optimize the lifespan of a battery, but the method just doesn't jive with people's typical usage.