Being unhappy is rubbish, I should know I used to be a right misery guts!! I've learned to be happy though and I'd love to pass that on to anybody out there in the world who needs a bit of apush start.
One of the keys to keeping happy is just to keep busy. Depression keeps us thinking about doing things and then worrying about what might happen and finally telling ourselves that there is no point in trying because it will never work! Failure seems like the worst possible outcome - and it also seems like it is ineviytable.
The way out of this is just to do something, anything! Tidy your living space, clean the kitchen, learn to play an instrument, draw a picture, write a poem, call a friend, alphebeticise your record collection, start a political party... It really doesn't matter what you do as long as you do something. You might get bored or give up after 20 minutes, no problem, have a rest, pick yourself up, dust yourself down and start all over again.
You'll find that one thing leads to another and soon you won't have to push yourself, you'll have the momentum to just keep going.
The ideal activity will be so engrossing that you will lose all track of time, like when you were a kid playing some game and the whole morning passed without you realizing it and you missed lunch! There's a book all about this called flow which goes into extreme detail about what types of things do this best, but it's generally hobbies and things where you can measure your progress. But you can make any activity a flow activity by making agame out of it.
And one thing leads to another and before you know it you are head of the local crocheting association and about to marry the teasurer... well, it might happen. If you don't start crocheting you will never know!