The phrase "don't give up the day job " means that you ought to keep doing what you are great at, instead of taking a stab at something new or turning your hobby into your profession.
Example of use: "I tasted the cupcake you baked yesterday. My feedback is: don’t give up your day job!"
Interesting fact about Don't Give Up The Day Job
This phrase is a combination of somewhat sarcastic with good-natured advice.
