One issue I'm dealing with personally is forward head posture.
This is when you neck cranes forward, putting your head above your chest or out in front of it instead of seated directly over your shoulders like it should be. There are a myriad of negative effects from this.
I've recently begun a serious attempt to address it. Along with the professional help I'm getting from a Physical Therapist, I've found these two videos extremely useful. In fact, I first picked up the stretches I'm doing for this condition in these videos, and then ran them past my PT who approved them all.
The first video is Christie Estadt of Body Blueprint.
The video is excellent and starts with a demonstration of forward head posture assessment.
If there is one thing that makes this video hard for me is that there is a guy in the background setting up for, and then doing, jump squats. That's a lot of movement not to glance at, and the trainer in me wants to watch every rep to ensure he is jumping and landing correctly. If you can tune that guy out (hard, now, I know, since I just told you TO LOOK AT HIM!) and concentrate on Christie's explanations, you can get some benefit from this.
The second video is from Elliot Hulse, of Strength Camp Online.
Elliot is very knowledgeable and his information is on point and well explained. He does love the F-word, though, so for those with sensitive ears, kids in the room, or checking this video out at work, be aware of that going in.
If you're struggling with this and you're tired of people telling you to do 3 sets of 10 chin tucks a day and pretending that's enough volume to undo 24 hours a day of neck posture issues, or saying "Just sit up straight," those might help.
And why doesn't "just sit up straight" work? Because you end up moving dysfunction to somewhere else (a back arch, shrugged shoulders, a bent upper back, just a lean back) to get the head into the "right" position. You aren't solving the problem, just taping something over it so you can't see it. It will come back as soon as you relax.