Environmental stress can be due to anything from a dripping faucet that's just a bit too loud to the complexities of peer pressure.
The two big categories are stress from the physical environment and stress from the social environment. The distractions and obstacles of the physical environment are direct and more easily noticeable. Overcoming them is also easier since the source of stress is relatively obvious.
Take a look at the places you spend most time in (such as your home or workplace), and make sure to set things up the way you want them to be. By personalizing your work environment it is easier to shut off distractions and get into the proper mindset.
Stress from the social environment is a difficult nut to crack; communication, tolerance, organizational etc. problems are everywhere and difficult to solve without dedication to raising awareness.
Perhaps the single most damaging source of stress is when you have different priorities than others around you. The priorities of society and the priorities of an individual are often different, and noticing these subtle differences requires conscious effort. Setting them straight within yourself requires a great deal of courage as well.