Akin to locking your doors and closing your windows there's some really basic things everyone should be doing with their Linux installs (This is of course written from a Fedora viewpoint, but I think this pretty much applies to all computer OSes).

1. Choose nice long passphrases you can remember. Most any modern system will have a pretty long limit on passphrases, so pick something nice and long that you can remember. Don't think of them as passwords, they are phrases with many words.
2. When installing, encrypt your drive(s). The performance hit is not noticeable and if you ever throw away a broken drive or someone steals your computer they won't have your data.
3. Apply updates regularly. If you aren't someone who remembers to do so, setup something like dnf-automatic to just apply them every day for you in the middle of the night. Otherwise try and get into the habit of letting gnome-software do offline updates at some regular time.
4. Along with (3), reboot when needed for new kernels or glibc or other things you use. Get used to rebooting on a regular schedule. Don't be afraid of rebooting, get used to doing it.
5. If you are in a place with untrusted people roaming around, do setup a screen locker and lock your computer when you are away from it.
6. Make (and sometimes test) regular backups. You may not think of backups as a security measure, but they sure are. Think of the new fad of 'ransomware' where someone encrypts your data and sells you the key. If you have good backups you can just wipe that all out and restore from those. They are handy for lots of other reasons too.
7. Don't open weird attachments or links sent to you in email. If you didn't ask for it, delete it.
8. Don't plugin weird devices you run across to your machine. (USB or otherwise). You can use a neat package called 'usbguard' to make sure no one else does while you are not around too.
9. Use a passphrase manager or have some system to allow you to have long, not easily guessed passphrases at all the various applications you login to. There's tons of these out there: Password managers: pass, keepassx, gpg encrypted file, etc. Schemes: Diceware, etc. Pick one that works for you.
10. If you use a laptop/travel a lot, consider using a VPN for all your network needs. As long as you have an endpoint to connect to (your home server, your work, a vpn provider) you can send (almost) all your traffic over the vpn and thus avoid problems with people sniffing local traffic.

Some of these things require an initial investment of time (backups, vpn, passphrase manager, screen lock) and some require just making something a habit (long passphrases, apply updates regularly, reboot regularly, don't open weird things in email or the physical world), but they are all worth it. Will this make your computer "secure"? No. There's no such thing. "secure" is not a binary state, it's a process of assessing threats and deciding what you can or want to do about them. Doing the above things will protect you from some threats nicely (guessable passwords, untrusted people tampering with your computer, sniffing traffic, vulnerabilities that have already been fixed in software you use, etc), but will basically do nothing against others ( someone installing a keylogging device and recording everything you type, someone threatening you with harm to tell them some information, someone installing a spy cam and recording everything on your computer screen, someone using a non public vulnerability in software you use, someone social engineering access to your computer, etc).