These are a few issues I've thought about enough to have a strong opinion on. I believe these principles provide a useful framework for making decisions, and that using this framework will ultimately make me happier.
As with anything created at the grand old age of 25, I'm sure this isn't the last thing I'll write about it, and I fully expect to edit, remove or add to these principles over time.
1. Simplicity is good. It saves mental power for other things (this is why Obama only wears two colours of suit, to save decision-making effort for more important issues than merely deciding what to wear).
2. Minimalism - a lack of commitments (financial or otherwise) and a lack of possessions - also reduces stress. Books are the exception to this rule.
3. As a corollary to rules 1 and 2, I am prepared to pay for quality - if I'm only going to have a couple of pairs of shoes, or 4 suits, I want them to be good quality.
4. Likewise, I'm willing to pay other people to do things I could do myself if it reduces stress and frees up time for other things - money is renewable, time is not.
5. Keeping your monthly outgoings as low as possible and maintaining cash on hand goes a HUGE way to reducing anxiety and increasing happiness. Corollary: eliminate and do not use consumer debt. It's like running with a parachute strapped to your back.
6. What people have actually ACCOMPLISHED is much more important than their qualifications. This is true for me as much as it is for anyone else.
7. Experimenting and tracking results is crucial to improving anything.
8. If we define "rich" as being able to buy anything you want, then there are two ways to do this: get more money, or want for fewer things.
9. Having said that, money is only one of three currencies: the other two, time and flexibility, are often much more valuable (see rule 4).
10. You can be good at more than one thing, and often it helps.