How do we achieve happiness? Is it a state you fade in an out of, or is it a permanent state of being?
I would argue that it's the latter. It's an everlasting emotion. It's something that is in and around everything we do. Happy people make other people happy without taking away from their own happiness; just like one candle lighting another. There will be ups and downs, but as long as your ship is sailing in the right direction, the waves won't matter. When we look back in life, we won't be saying to ourselves, "How many houses did I buy?" "How many cars did I drive?" "How many people have I slept with?"
What we will be saying however are things that touch on the deeper side of what being alive is all about; "Did I live?" "Did I love?" "Did I matter?"
Strive towards your goals. Set time oriented and measurable goals, and achieve them. One gains a much greater sense of accomplishment from striving toward some specific, measurable thing than from striving to reach some general area.
Smile more, always. Whenever you walk into a building, smile and say "How's your day going?" to anyone that serves you. You will shortly find that people will become much more friendly, and hence much more likely to do what it is you ask of them, if you simply ask them how their day went prior to your arrival.
Recognize how fortunate you are to be alive. Study those who are less fortunate and then be astonished at your own luck. This one seems kind of perversed, but when we consider that the vast majority of the world's population lives in poverty, amongst many other dire circumstances, our existence becomes one to be cherished.
Materialistic things bring some happiness, but then we adapt to that level of materialism and then we are not satisfied with our current condition; this is always the case. This is referred to as hedonic happiness, or as running on the hedonic treadmill. It is the tendency of humans to relatively rapidly return to a constant level of happiness despite major life events.
Meditate and do yoga; cultivate your inner awesome. We all know about "working-out", but how much do we know about "working-in," as coined by Paul Chek. We need to cultivate our energies if we wish to later expel them throughout the various tasks of our daily lives. We cannot always be producing without ever regenerating our energies. You can also calm your mind by doing Qigong, Tai-Chi, having sauna sessions, getting massages, making love or partaking in various other relaxing mind-body experiences.
Go out and do these things, and watch your life change:)