Nothing in particular for traps. I used high pulls a lot. That and lots of slow shrugs for time under tension.
One thing people miss is that trap muscles are kind of fan shaped. So, instead of dragging the dumbbell straight up your legs for shrugs, try to use a little bit of rearward motion. Visualize it as trying to get your shoulder slightly behind your ear instead of in your ear canal.
You can also combine a 60 second suitcase carry with a set of mild upright rows. At max height keep the weight between your sternum and nipples for shoulder safety. You get a long weighted stretch that can benefit hypertrophy and counter act a little bit of the performance issue that comes with long stretches. Just be careful with the weight, watch for signs of stress on the cervical spine, and try to follow the natural path of the muscle.
Dumbbell clean and press may also help, but it is a full body exercise and you should start light until you get the groove.
Edit: When doing trap work don't roll your shoulder forward at the top. I know some people do shoulder circles while doing shrugs. I recommend against it because when your trap is completely contracted you're adding a stretch to the muscle. It can lead to neck pain or worse if you get too extreme with it. There are a ton of small muscles in the posterior delta that work to support and add mobility. You could over stress one and lead to nagging issues.