I have brought my rear delts, and upper back up a ton this past 12 months by implementing some of these things
Hit up some scapular retraction work for the upper back. Something like a hammer strength low row(or seated close grip cable row), keep arms fairly straight with just a slight bend at the elbow, and bring the weight back by retracting your scapula. Don't shrug up, but shrug back. This will also help you on the bench as it will help keep those shoulders back. Throw in 3 sets at the end of your workout a couple times a week, fairly high reps.
IMO rear delts/upper back can handle a lot of frequency, and volume. At one point I was doing upper back, and rear delts almost every workout. Nothing too serious, but just getting some blood in there
Pick a weight do 50-60 "swings", cut the weight in half do 30-40 more, cut the weight in half again, and do 10 full range of motion. Valdez can tell you how fun these are..lol
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Can do these on a chest suported tbar. Key is keeping the elbows up/flared.
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I like supersetting these with another movement. So say a pressing movement followed by 10-15 of these. Or side laterals supersetted with these.
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Face pulls or a variation like this.
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These are nice too. Just change it up all the time.
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