This one seems weird at first, speaking from first hand experience, but it is one of the simplest things and can make such a difference in your day. Actively trying to smile more. Several years ago I started doing this because I had been described as unapproachable, when in reality I just have a resting bitch face. I started making an effort to smile more, and like magic people started approaching me. The simple act of smiling a bit more has lent itself to new friends, new opportunities and just better days.