Most of the time if your computer is overheating you need to blow it out with a can of dust. I recommend to blow your computer out every month sometimes more regularly depending on where you store it. Do not store your computer on the floor. It pick up the most dust there.
Doing regular virus scans.
Keeping everything up to date. – this is easy if you have a very minimal ammount of programs
Use a NAS for storage. – Synology NAS is probably where you should spend all your money. Keep your hard drive space for games.