Nice post. It seems like a good summary of important results from happiness science, with interesting ideas about how to increase one's social skills added. Some comments:

So which personality traits tend to correlate most with happiness? Extroversion is >among the best predictors of happiness,22 as are conscientiousness, >agreeableness, self-esteem, and optimism.23

I'm surprised that you don't mention the trait neuroticism, which in many studies has the strongest correlation with happiness. (see eg) In general, neuroticism and extraversion are far better predicators of happiness than conscientiousness and agreeableness (even if the latter traits have some effect).

One benefit of religion may be that it gives people a sense of meaning and >purpose

Interestingly, religion doesn't correlate with happiness in more athestic (compared to US) european countries like Sweden. One way to explain this is that much of the effect is socially mediated and that less of the effect is meditated by finding meaning in life.

Many people report that constantly checking to see if they are happy actually >decreases their happiness

Do you know of any studies showing that checking if you are happy reduces happiness? As far as I know very few empirical studies have been done and this idea is mostly based on philosophical speculation by people like J.S. Mill and Sigdwick ("The paradox of hedonism").