Here are some lessons on how to be happier:

1. Don’t start with profundities.
When you began your Happiness Project, One should start with the basics, like going to sleep at a decent hour and not letting oneself get too hungry. Science backs this up; these two factors have a big impact on happiness.

profundities means  the quality or state of being profound or deep.

2. Do let the sun go down on anger.
Don't always scrupulously aired every irritation as soon as possible, make sure you vented all bad feelings before bedtime. Studies show, however, that the notion of anger catharsis is poppycock. Expressing anger related to minor, fleeting annoyances just amplifies bad feelings, while not expressing anger often allows it to dissipate.

scrupulously means acting in strict regard for what is considered right or proper.

vented means to relieve oneself by venting something (as anger) <comes home from work and vents to the kids>.

catharsis means eliminate anger.

popycock means nonsense

dissipate means vanish or disappear

3. Fake it till you feel it.
Feelings follow actions. If you're feeling low, you deliberately act cheery, and  find yourself actually feeling happier. If you're feeling angry at someone, do something thoughtful for her and your feelings toward her soften. This strategy is uncannily or surprisingly effective.
uncannily means being beyond what is normal or expected.

4. Realize that anything worth doing is worth doing badly.
Challenge and novelty are key elements of happiness. The brain is stimulated by surprise, and successfully dealing with an unexpected situation gives a powerful sense of satisfaction. People who do new things — learn a game, travel to unfamiliar places — are happier than people who stick to familiar activities that they already do well. Often remind yourself to “Enjoy the fun of failure” and tackle some daunting goal.
daunting means tending to overwhelm or intimidate

5. Don’t treat the blues with a “treat.”
Often the things you choose as “treats” aren’t good for you. The pleasure lasts a minute, but then feelings of guilt and loss of control and other negative consequences deepen the lousiness of the day. While it’s easy to think, I’ll feel good after I have a few glasses of wine…a pint of ice cream…a cigarette…a new pair of jeans, it’s worth pausing to ask whether this will truly make things better.

lousiness means poor or inferior

6. Buy some happiness.
Our basic psychological needs include feeling loved, secure, and good at what we do and having a sense of control. Money doesn’t automatically fill these requirements, but it sure can help. Learn to look for ways to spend money to stay in closer contact with your family and friends; to promote your health; to work more efficiently; to eliminate sources of irritation and marital conflict; to support important causes; and to have enlarging experiences. For example, when your sister got married, splurged on a better digital camera. It was expensive, but it gave you a lot of happiness bang for the buck.
splurged means to spend extravagantly

bang for the buck means more or bigger

7. Don’t insist on the best.
There are two types of decision makers. Satisficers (yes, satisficers) make a decision once their criteria are met. When they find the hotel or the pasta sauce that has the qualities they want, they’re satisfied. Maximizers want to make the best possible decision. Even if they see a bicycle or a backpack that meets their requirements, they can’t make a decision until they’ve examined every option. Satisficers tend to be happier than maximizers. Maximizers expend more time and energy reaching decisions, and they’re often anxious about their choices. Sometimes good enough is good enough.

8. Exercise to boost energy.
I knew, intellectually, that this worked, but how often have I told myself, “I’m just too tired to go to the gym”? Exercise is one of the most dependable mood-boosters. Even a 10-minute walk can brighten my outlook. 

9. Stop nagging.
You might think nagging will help you but quitting nagging will help you boost your happiness. Instead of nagging why don't you use other persuasive tools: like wordless hints, using just one word, not insisting that something be done on schedule; and, most effective of all, doing a task myself. Why did I get to set the assignments?
nagging means to irritate by constant scolding or urging.

10. Take action.
Some people assume happiness is mostly a matter of inborn temperament: You’re born an Eeyore or a Tigger, and that’s that. Although it’s true that genetics play a big role, about 40 percent of your happiness level is within your control. Taking time to reflect, and conscious steps to make your life happier, really does work.