If happiness is the opposite of suffering, then the key to happiness is knowing the four noble truths and following the eightfold path:
Four Noble Truths
1. Life is suffering
2. Suffering is attachment
3. Attachment can be overcome
4. There is a path for accomplishing this - the eightfold path
The eightfold path
1. Right view is the true understanding of the four noble truths.
2. Right aspiration is the true desire to free oneself from attachment, ignorance, and hatefulness.
These two are referred to as prajña, or wisdom.
3. Right speech involves abstaining from lying, gossiping, or hurtful talk.
4. Right action involves abstaining from hurtful behaviors, such as killing, stealing, and careless sex.
5. Right livelihood means making your living in such a way as to avoid dishonesty and hurting others, including animals.
These three are refered to as shila, or morality.
6. Right effort is a matter of exerting oneself in regards to the content of one's mind: Bad qualities should be abandoned and prevented from arising again; Good qualities should be enacted and nurtured.
7. Right mindfulness is the focusing of one's attention on one's body, feelings, thoughts, and consciousness in such a way as to overcome craving, hatred, and ignorance.
8. Right concentration is meditating in such a way as to progressively realize a true understanding of imperfection, impermanence, and non-separateness.
The last three are known as samadhi, or meditation.
From The Basics of Buddhist Wisdom
Dr. C. George Boeree