A) Know what they can use to detect that you're in their systems
B) Know what they can use to link it back to you
From these two points you narrow down the chance of being caught.
You could hack an old machine, for example, since reconnaissance is the most important part of hacking, and you got access to it all. In case you get caught they wouldn't think it was an insider.
But be safe, if you don't master what you are doing, you'll be caught.