In practice I see many people with headaches and neck and shoulder pain. Many times it comes back to poor posture and head positioning. Improving your posture goes a long way towards reducing pain in the shoulders and neck, and awareness is generally the first step. I always encourage active care, and below are a few simple (but important!) exercises and stretches you can do.
Chin retractions/tucks. A lot of people sit with their heads too far forward, which increases the load through the neck and causes muscle tension in the upper trapezius muscles and the group of muscles that sit under your skull. A good corrective stretch is the chin tuck - draw your chin back without looking down, hold for ten seconds then push your chin forward. Do three repetitions, as many times a day as you like.
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Upper Trap Stretch. Place your right arm behind your back (or sit on your hand) to anchor the shoulder. Tilt your left ear to your left shoulder. Rotate your nose towards your shoulder - somewhere in that arc you'll find a band of tight muscle and that's where you want to hold the stretch. Hold for 20-30 seconds. You can increase the stretch by resting your left arm on top of your head, but DO NOT pull. Repeat on the opposite side.
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Pec Stretch. Place your palm onto a door frame at about head height with your elbow bent. Slowly turn your body away from your palm until you feel the stretch in your chest. Hold for 20-30 seconds. Repeat on opposite side.
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Self Massage. Place a tennis ball or similar into a long sock. Sling it over your shoulder and lean up against a sturdy wall. Roll on the ball along the muscles between your shoulder blade and spine. If you find a tender spot, hold pressure against the ball for about 20 seconds then keep rolling. Repeat for the muscle on the back of the shoulder blade (this one can be quite tender/painful - go easy)
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As always, please let me know if you have any questions.