This is a guide to a longer lasting Android device, from choosing one to how to preserve the life of the one that you have.

Choosing a long-lasting and repair friendly phone:

To get the best shot at longevity, start with a high quality device from a manufacture with a history of long term device support, and one that regularly releases there modifications to the kernel source code. A device that has an unlockable bootloader (XDA developers Forums is a good place to see about ROM support), and is user repairable (See iFixit's Smartphone Repairability Scores) will allow you to keep the software & hardware going the longest. Both the Google Pixels, and Fairphone's line are a good place to start. Fairphone is the USA is sold though Murena

Before you use your phone

• Get a good sturdy case like an Otterbox
• Apply a screen protector. I recommend Glass, Sapphire is the best (but very expensive).

Battery

Lithium-ion (LI-on) battery's wear out faster when near the upper and lower charge levels (read why here: Battery University), so avoid charging or discarding the battery fully, aiming for around 20~80% is a good target.
Never leave your phone in a hot car or in the Sun, extreme heat exposure reduces the lifespan of the battery & is generally bad for other components.

Charging

• Avoid fast & wireless charging by using a older charging block that only outputs a few(1~2) Amps. (to reduce the heat the battery endures)
• Use a magnetic charging cable to reduce the wear on the plug (Like Volta), you need a bulky case to have it flush to not make the phone uncomfortable to hold though. 
• When/If you use a regular charging cable don't move the phone around when it's plugged in, movement wears the plug much sooner.

Use a charge limiting feature. (Listed in order of recommendation.)

1. If your phone has a built smart battery charge management feature, use that. (Most modern high end phones do, including Samsung's, Google's & Apple's)

2. If you have Root; use ACCA(a GUI for ACC) (Suggested Charging config: Level limit: 85%, Current: 700mA, Voltage: 3800mV)

3. Buy a switch that can wirelessly cut off power based on charge level:

• A Chargie by Lighty Electronics is a Bluetooth enabled USB-A power switch, the accompanying APP configures it to auto cut off power based on power draw or charge level. Note that in the newest Android versions/PlayStore restrictions prevent versions of the APP past v2.2.20 from auto enabling Bluetooth, making this solution a little less appealing as you have to leave Bluetooth on you manually enable it.
• Using an Automation APP like Tasker to turn off a Home Assistant-controlled smart plug when the battery exceeds a reprogramed threshold, is a more reliable method & works for any device.

4. Install an APP that alerts you at charge levels so you can unplug you phone. (AccuBattery, Battery Guru: Monitor & Health, etc.

Waking & Locking the screen

To reduce the use of the power button, as it's a fail point, although less common.

To wake 

 1. Use the features "Lift to check phone/events" and "Double-Tap to check phone"

 2. Use the fingerprint reader to wake and unlock.   

To lock/turn off the screen  

 1. Use a launcher that support double tapping the home screen to lock it (Nova launcher, Smart launcher, etc.)

 2. Use Googles Quick Tap feature if you have a Pixel or the APP Tap, Tap for any Android to lock the screen. (Note: battery life might suffer)  

 3. Use a short Screen Time out.

TIPS

• Get a new case to get a fresh look and feel when your tired of the one you have.
• Read through the comments! There are many good additions from people with different experiences & perspectives.

Edit's: Updated & reformatted several things based on comments <3