The term "laptop" is a bit of a misnomer as using your computer on your lap can be dangerous;
Laying your device on the bed can prevent adequate cooling and can shorten the life of your device - for laptops, use a laptop tray.
Avoid touching the screen (with anything! - unless it is a touchscreen model). Hold and lift the laptop by its base, not by its LCD display (the screen).
Make sure you never leave pens or pencils on your laptop when you close it - doing so will break the screen.
While the toughened glass on the fronts of tablets may boast of being "scratch proof" the reality is that they are more "scratch resistant" - take care to protect the screen both in use and in your bag.
A good cover with a flap across the screen is a great idea.
Do not have liquids, especially sweet, sticky drinks like soda, nearby when using your laptop. Spills can cause serious damage to the machine and can be costly to repair.
You would be surprised what grows on the food crumbs that get lodged under the keys of your keyboard! This is not just a health issue though - they can also work their way into the internals of you computer and result in costly repairs.
Pet hair and dust can clog the cooling systems vents and fans and cause overheating. Ideally keep the computer in a clean and dust free room.
Do not pull on the power cord, pull on the plug to remove from a socket. Avoid rolling your chair over the cable as that can break the wires inside. Also be aware of how hot your power supply can get so do not use it on a soft/flammable surface or covered.
Take care when plugging the charging cable into the device as the ports are often small and delicate.
And in the right orientation!
Not only does that invite thieves but on sunny days the temperature in a car can cause irreparable damage to your device.
Avoid crushing your laptop by stuffing too many books around it inside your backpack. Avoid placing heavy materials, such as books, on top of your device.
Today's Lithium ion batteries can handle many charge/discharge cycles. To maximise their life it is best to try and keep them in the top half of their capacity. Repeated deep discharging of these batteries reduce their capacity and lifespan. If there is a power point available it is best to use it - often this will also mean the device can perform better too.
Keeping your device software up to date is one of the best ways of avoiding viruses and malware.
While some OS's (operating Systems) automate the process by default - Chrome OS (Chromebooks) some require you to either manually update or set up an Auto-update feature (windows, OSX). Others will require periodic (often annual) manual updates (Android iOS).
Be aware of what your device requires. Update as necessary.
While it is a good idea to have Anti Virus/Anti Malware running at all times, and have them regularly scan your whole device, you can prevent most issues yourself by practicing a safe approach to computing.