Well Solveig, very good question. Let me throw some suggestions out there.
1. Let it go – Constantly shit happens in life. Constantly annoying things occur. Now, deal with them as much as you can and don’t just give up, but when it’s done it’s done. You need to let the past go and move on. It’s very hard sometimes, but otherwise you are just tormenting yourself for no reason. This brings me to my second point:
2. Don’t accept your failings, your inabilities and always try to improve. At the same time, forgive yourself for them – they are you and your ability to change is limited. You will see many people who do the inverse – they don’t try to change but are constantly upset at themselves for their shortcomings and feel bad about it. This is very important! Both sides – try to improve but forgive yourself.
3. Look at the people who surround you – are you happy with them? Try to remove cancerous beings from your life. Sometime you work with them, think of changing jobs to a place you will work with better ones. Sometime it is old friends you feel uncomfortable to drop – do they really want what is best for you, or do they act from envy or other misplaced motives. Especially when giving you advice, do you think they really care about you. If they are family members it is hard, but sometimes you just need to know to get away from there to where you will make up your own mind on things and do what is best for you.
And then, boyfriend/girlfriend: it doesn’t simply matter who is that person in the world but how they are for you. Does s/he improve you, make your life better, or worse. They could be the greatest but unless they are a good fit, it is better to think it over.
Surrounding yourself with the right people will make a HUGE difference for you. And thus we arrive at point 4.
4. You surrounded yourself with good people, now also, listen to them. Talk to them. Don’t simply keep it all quietly inside, but try to let it out. Try to express yourself as keeping things bottled up is one of the worst things for happiness. Feel you can share with them your life.
5. Laugh! Make sure to laugh a lot, try at least once a day, the bare minimum. Smile. Don’t let yourself drown in the daily grind.
6. Try to find time to do things that will give you energy. Not simply momentary things that will make you happy like eating ice-cream, shopping and the like, but deeper things to actually renew interest in the world. Go to the cinema, read, whatever you know gives you energy in the world. This might take a while. It is not immediate, but helps a lot in the long run.
7. Always continue developing. People tend to give up on developing when they reach a certain age. You see them smiling a lot less. Try to continue to develop all the time, even when you are 80. Never give up on that.
You might want to see Mike Leigh’s Happy Go Lucky which goes through some these points nicely.
Ok, I guess that’s my 2 cents. Hope it helps :-)