Better safe than sorry This idiom is used to recommend being cautious rather than taking a risk.
Bite off more than you can chew
If you bite off more than you can chew, you take on more responsibilities than you can manage. 'Don't bite off more than you can chew' is often used to advise people against agreeing to more than they can handle.
By the book If you do something by the book, you do it exactly as you are supposed to. Brush under the carpet