Mindfulness
I've learned the importance of really paying attention to what I do, how I do it, and why. It goes beyond paying attention. To illustrate, if you're performing a task, focus fully on the task rather than allow your mind to wander about trivial things. If you're at dinner, focus on the person sitting across form you. One of the benefits of being an introvert, is being able to observe the environment, and the people around you. Often times, the quietest person in a group seems disconnected from everyone else, but in actuality they're the most engaged. For me, this is because I'm observing body language to really understand what's going on.

Twenty-Minute Rule
I often spend a few hours a night performing mindless tasks, since I usually need to wind down at the end of the day. Like shutting down a computer, all of the background processes have to turn off before it can completely shut down; otherwise, I can't sleep. The downside is that this turns into a few hours, and I end up staying awake longer than expected. If I replace these hours with 20 minutes of productive activity (Usually, I catch up on news or current events, writing etc.) I have an easier time switching gears and sleeping when necessary.

What about you? have you discovered any useful but small lifestyle changes that have long term impact?