The way I define happiness is being the creator of your experience, choosing to take pleasure in what you have, right now, regardless of the circumstances, while being the best you that you can be.
Deal with something once. Do it now. Then it’s off your mind, and you can fully focus on the next matter.
When the task takes only 5 or 10 minutes I recommend to do it immediately, even when you are busy. Once you’ve done it, it isn’t stuck in your mind and you have less to worry about.