Don't store any personal information on the company computer.
Anything you do, they may be able to monitor, back up, recover, etc
Don't look at porn on the company computer, Don't use Facebook on the company computer, don't like sketchy models on Instagram from the company computer.
If they just gave you a computer budget, and then ask you to return the computer at the end, and they don't run any of the software... You could use full disc encryption, and then reformat put a new key on it when you return it. You could just take the disc out, and replace it with a new disc when you return it