To try and find a simple answer to a complicated question is tough. Ask 50 people and get 50 different answers.
I myself when I sit I like to sit facing the front door preferably next to a window (doors are not the only outs) but not in front of it (ya never know what comes through it) and I don't like people walking behind me like next to the kitchen door. The threat can come from anywhere so the best thing it to mentally map the place out on your way in.
I live in Texas so the luby’s shooting in Killeen ever present as is the McDonald’s shooting in California. To say it will never happen is to be in denial but to stop living because it might is even worse