I started to notice a pattern of more fearful fliers having a fear of claustrophobia lately. One interesting thing to keep in mind is that most of the major air carriers have been contracting out more flying to regional airlines that fly smaller regional jets. Some of these regional jets carry from 35 to 90 passengers, but they are still narrow in the cabin compare to mid size jets like the Boeing-737, or Airbus 320. However, there are three basic steps you can take to combat claustrophobia.
One step is to always fly in the front of the cabin. Why? This gives you the illusion of more space. For instance, if you sat in the back of the cabin you will see row after row of seats with little peripheral vision which will constantly remind you that your in a narrow tube.
Step two, fly on discount carriers & no, I am not saying so because of favoritism. The reason I recommend discount carriers is because they usually fly to more secondary cities & they usually don't contract out to regional airlines. So, for example if you departed out of  secondary cities such as Manchester, NH versus Boston, or White plains, NY versus Laguardia you are more likely to get a direct flight & cheaper flight. Also, another reason to fly on discount carriers is that they don't have regionals affiliates. Southwest, Airtran, Allegiant, Spirit, & Jetblue all fly their own aircraft which are mid size aircraft. Jetblue is one exception that fly a regional jet such as the -Embraer- 170, however it has more leg room than most aircraft of the same category.
Finally, the third step is try to pick a flight that is have full so that your have a better chance of getting a row to your self. A plane that is half full is also going to have better cabin air. Cabin air is constantly being recirculated. Less passengers mean more quality air which will help you breathe more comfortable.