Have enough money to live. Having good status is more important than cash - it's relative income that makes the main difference
Desire less. A good Stoic principle. To quote New Scientist: In surveys by the Roper polling organisation in 1978 and 1994, for example, Americans were asked to list the material goods they thought important to "the good life". The researchers found that the more of these goods people already had, the longer their list was, so the good life remained always just out of reach.
Intelligence (in terms of IQ) isn't a factor.
Your genes account for a large chunk of your general level of happiness. Also, extroverts are happier, and happiness makes people more extrovert
Think of yourself as attractive.
Have a good network of friends / family
Believe in a religion
What I say
Do happy things, think happy thoughts. This is a simple principle, but it's the principle behind "Cognitive-Behavioural" approaches, which are proving to be the most effective in treating illnesses such as depression, social phobias and even psychosis (BMJ article). So, listen to some happy music!
Ensure you're eating enough Omega Three Fatty Acids. Basically, the membranes in your brain cells are constructed of fats. If your body has these "Omega-3" fats available it uses a high proportion of these to build the cell walls. If not (e.g. you're living on junk food) then it will use the other fats available (e.g. those from that Mc Donalds you ate...). There's a lot of evidence that adding Omega-3 to your diet makes you more intelligent, calmer and happier!