Keeping with this week's theme of things I've learned from the last year or two, here's something a bit more personal.
I'm a lot happier than I was two years ago. There are a few reasons for this - I'm better off, I'm socialising more, my PhD is closer to being over - but I think the main one is that I've come to understand happiness a bit better than I used to.
Happiness isn't a thing or set of things to you try to acquire. It's not something you possess. It's a thing you do, or better yet a property of (some) things you do; it's an adverb ('I happily play piano and guitar', 'I write happily' etc.).
I think I've said before (and if not here then at least elsewhere) that my PhD is on what's called phenomenalistic idealism, the metaphysical/ontological position that the universe is ultimately composed of experiences. The details of the position aren't important for now. I bring it up because I'm starting to find phenomenalism really useful outside of metaphysics as well (it makes for a great literary technique, too, but that's a topic for another time).
For present purposes, the key point is this: happiness is a kind of experience, or perhaps a property of some kinds of experience. Even if your idea of happiness is lazing in the sun and not doing anything, it's still your experience of that which actually brings you happiness.
And experiences are always present. They're always what's happening now. A memory can only bring you happiness if you recall it - bring it back out of your past and into your present experience. And future experiences bring very little happiness at all. The pleasure of daydreaming of some future success is only ever a pale shadow of the happiness that actual success would bring.
The key to happiness, then, is to work out what kinds of experience make you happy. For me, at the moment, it's making music, telling stories, and good company. Those aren't the only options - perhaps yours might be sporting, or sexual, or familial - but they're the ones that matter to me. And I've learned to make decisions that maximise those activities.
Because my PhD is coming to an end, I'm having to start making decisions about the future (like the continuing, ever-harder decision not to attack all the people who ask me 'What can you do with that degree?' - take this as a warning. Please.), and making those decisions in experiential terms has been surprisingly liberating. I've realised that I need relatively little money in order to keep writing and making music, and the cost of good company comes in terms of time, not money, so I'm happy for the next year to keep working my sporadic and unpredictable part-time job and keep the rest of my time for other things. I don't want to stop working altogether because I don't want to face the experience of having to explain an employment gap to potential employers. I don't want to look at buying a house because I can't see anything that it would add to my experience (at least, right now) that I actually want.
So my recommendation is this: when you're making decisions of all kinds, ask yourself about the experiences that will result from your choices. If you decide to get a particular job, ask yourself what it will involve doing every day. If you're looking at buying stuff, buy experiences, not just objects (which doesn't necessarily mean that you shouldn't buy objects which enable you to have experiences you want - you may really want the experience of wearing fancy shoes or driving a fancy car, and that's fine, but remember it's the experience that counts).
And remember, too, that the costs of things are experiences, or have experiential consequences. If you have to give up one experience in order to afford another, balance the two. Don't think of money as a number - think of it as representative of experiences you're trading away. All through my childhood I failed to consider this angle, and as a result I ended up buying a mountain of crap toys that only brought about five minutes' enjoyment with them each. Growing up is in part a process of learning not to make that mistake.