Where the NT directly contradicts the OT, go for the NT passage. I'm thinking specifically about forgiveness, diet, etc).
If the NT is silent on a subject the OT has the final word.
Indeed All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: (2 Timothy 3:16) Which at that time was the OT. But NT silence itself does not necessarily mean something in the OT does or does not have its observance abrogated, for the NT deals with such as classes, not only specifics, as in affirming universal moral laws while abrogating the literal observance of ceremonial laws and temple ordinances, as in
"meat, or in drink, or in respect of an holyday, or of the new moon, or of the sabbath days: Which are a shadow of things to come; but the body is of Christ." (Colossians 2:16-17)
Which stood only in meats and drinks, and divers washings, and carnal ordinances, imposed on them until the time of reformation. (Hebrews 9:10)
Meanwhile the intent of all these laws are to be fulfilled by those who are justified by heart-purifying regenerating faith,
That the righteousness of the law might be fulfilled in us, who walk not after the flesh, but after the Spirit. (Romans 8:4)
But there is no law requiring all Windows users to switch to Linux - or vice versa! Thank God for options.