To isolate and build your trap muscles, dumbbell shrugs are an excellent exercise. You can do these with either a barbell or dumbbell.
Grab a dumbbell or barbell from the weight rack
Ensure that your arms are extended while you are upright with chest forwards.
Lift the weight upward and focus on engaging your shoulders while keeping your arms extended
After a pause, slowly lower the weights to the start position.
Once completing your set, re-rack the weights.
Keep the weights moderate to low if needed to engage the muscles properly.
Shrugs can also be done with a barbell, resistance band and a modified pulley as well.