While I could cite all kinds of scientific studies (like this one!) that claim meditating has psychological benefits that enhance a person's intelligence, ability to relax or produce chemicals that counter depression, I'm interested in taking this in a different direction, which is to look at the effect that awareness has on my happiness and my mood.
I've been spending most of my energy learning two types of meditation through the DC Shambhala Center. Shamatha, or "calm abiding," aims to pacify an agitated mind and develop mindfulness. Vipashyana or "insight" meditation, was taught to me slightly after Shamatha, and the aim of this technique is to develop greater awareness of the world around you.
By enhancing mindfulness through attention on the breath, Shamatha enhances a person's ability to focus and concentrate, so practicing Shamatha could help your mental endurance, like reading without getting disctracted or listening more carefully during conversations. Meanwhile, vipashyana enhances a person's awareness. This awareness can come through the physical senses, but it can also relate to a mental or even spiritual level of awareness.
To make an analogy on mindfulness and awareness, when a waiter serves you, it is mindfulness that allows him not to trip and drop the serving tray. But it is through awareness that he knows which table he is walking to or the quality of mind and manner with which he offers you your meal.
In my experience, mindfulness can develop quickly through meditation. Some people realize that they get more done at work without taking a lot of Facebook breaks, for example. But awareness is more elusive. You can't always be sure if you are gaining awareness or not because it usually has a more subtle and less measurable effect on your life. At the same time, we could come up with some examples in which we notice new awareness. You might be in the middle of a passionate discussion and realize that you are being aggressive. You might be standing outside in Autumn and realize it is cold and that the cold air feels nice on your skin; at the same time you may have a sudden and very physical realization that summer is over. All of that is awareness manifesting and growing in your life. Awareness is almost like a skill, but a skill that you can lose instantly, by getting caught up (again) in your narrow worldview, or by running from painful, scary reality.
So what does this have to do with happiness, you ask? Quite a lot, when you analyze it from the perspective of interdependent factors, including discipline and making choices. Let me give an example from real life...
On the weekends, I often wake up and don't feel like meditating. If I've been drinking with friends the night before I often wake up not feeling like doing anything that requires a finger-lifting ounce of exertion. In my state of morning mental weakness, I'm likely to jump straight onto the computer. Then my email might lead to me looking at some stuff I've wanted to buy. I end up screwing around on the internet for an hour and realizing I'm hungry, I haven't taken a shower, I still haven't meditated, I still have to do laundry and going to the gym probably isn't going to happen at all.
On the other hand, I often find that my day goes much better when I meditate first, and I think this is because my awareness is sharper after meditation. After meditating I usually don't get seduced by my computer or the television. I'm more likely to make good decisions, like making a healthy breakfast, followed by a shower (always a good idea) and planning out my day. By having the awareness or presence of mind to be disciplined about my meditation practice, I enhance my awareness. When my awareness is enhanced, I have a better gut feeling that leads me to do things that make my day progress smoothly. When my partner makes an annoying comment, I'm more likely to leave it alone. Discernment arises naturally from my awareness, not as a struggle of logical analysis. As a result, I feel on top of things, I have a reasonable level of control over the details of my life, and hence, I'm in a better mood.
This example is a microcosm of what greater awareness can do and why it is a good idea to work on building your awareness. On the flip side of the example above, if my awareness is strong I will sometimes start to do something that doesn't feel right, and instead of kicking into autopilot, I have the presence of mind (sometimes) to change course. That feels empowering, out of which confidence can grow.
After saying all of this, I better not blow off my meditation tomorrow morning! Whatever I do, I'll try to pay attention to the decisions I make and watch the process of karma unfolding.