Last week I talk about Upper Crossed Syndrome, aka forward head posture, aka texting neck. Being aware of where your head should rest on your body is a good first step in correcting the problem.
A solid second step is to work on the muscles in your back. My favorite go-to exercises are classic cable row or TRX row . The cable row is great because you can track your progress as you get stronger. The TRX row (pictured below) is excellent because you can work on core strength together with back strength. Double whammy.
A close runner up, is the cable rope face pull. This will also help with caveman arms, which I will talk about next week.
I strongly suggest throwing isometric core awesomeness (like planks) into your regular workout. As well as keeping up a ratio of 2:1 back to chest exercises.