In order to develop really great posture, it is essential that you include some upper back exercise into your program. This will not only help to straighten out the shoulders so you don't take on a rounded appearance but will also increase your bicep strength. Since when you perform upper back exercise often you also call into play your biceps, including such resistance training movements will help give you a more total workout.
When performing any upper back exercise, it is really important that you always think about keeping the head lifted. If you are looking down or to the side while doing it you may create additional strain on your neck. This could create a great deal of soreness or even a muscle pull if you start lifting very heavy weights.
Since upper back exercise does usually place a lot of stress on the body as there are quite a few muscles to be worked, be sure to take at least a day of rest after you do a hard workout as well. If you are feeling particularly sore you may wish to look into getting a massage treatment as those can really help to loosen up the muscles in this area of the body. Professional athletes are constantly getting regular massages because of this reason and to reduce any inflammation they get from their heavy training loads.
Lastly some simple shoulder rolls at the end of your workout can help to relieve any tension that has developed. Think of squeezing them up towards your head then pressing them down as far as they can go. Then squeeze backwards, hold that position and then release. Even doing this throughout the day while at work can be a good stress reducer and help you to stay focused. When you are sitting in front of a computer all day you naturally tend to shrug your shoulders, which can throw the whole spine out of alignment if this position is held long enough.