God’s Word gives clear instruction in both precepts and principles. Examples of a precept would be: no sexual immorality, do not repay evil for evil, pray without ceasing, in all things give thanks.
Principles are judgment calls. The Bible doesn’t mention cards, makeup, movies, or tobacco. The more you know about God’s Word, the better judgment calls or decisions you can make.
Another example of a precept is a sign that says “35 MPH.” There’s no give or take in that. “Drive carefully,” however, is a principle since it can vary with road or traffic conditions.