Eric Kim (via Vanessa) has some pretty good tips, drawn from the work of master street photographer Henri Cartier-Bresson. Perhaps my favorite one is “stick to one lens”:
Although Henri Cartier-Bresson shot with several different lenses while on-assignment working for Magnum, he would only shoot with a 50mm if he was shooting for himself. By being faithful to that lens for decades, the camera truly became “an extension of his eye”.
Apply the same mentality to when you go out and shoot. I encourage people to use different focal lengths to see the world differently and experiment—but ultimately sticking with one focal length will help you solidify your artistic vision. You will be able to see natural framelines in your everyday life, and know exactly how your photos will appear when shooting from certain angles and distances.