These work for me; they may work for you.
1. Avoid unhappy people. Most of them live in hells of their own devising; you cannot help them, but they can harm you.
2. Avoid negativity. Squelch negative and useless thoughts as they arise. Your mind is your domain and you have (limited) control over it. Don't dwell on the limits; push against them and expand them. Refuse entry to all unwanted guests. With practice, the power of the mind to control itself can be developed.
3. Set aside one hour per morning for formal meditation and the ruminative reading of high-grade self-help literature, e.g., the Stoics, but not just them. Go ahead, read Seligman, but read Seneca first.
4. Cultivate realistic expectations concerning the world and the people in it. This may require adjusting expectations downward. But this must be done without rancour, resentment, cynicism, or misanthropy. If you are shocked at the low level of your fellow human beings, blame yourself for having failed to cultivate reality-grounded expectations.
Negative people typically feel well-justified in their negative assessments of the world and its denizens. Therein lies a snare and a delusion. Justified or not, they poison themselves with their negativity and dig their whole deeper. Not wise.
Know and accept your own limitations. Curtail ambition, especially as the years roll on.
5. Blame yourself as far as possible for everything bad that happens to you. This is one of the attitudinal differences between a conservative and a liberal. When a conservative gets up in the morning, he looks into the mirror and says, "I am the master of my fate; I am the captain of my soul. What happens to me today is up to me and in my control." He thereby exaggerates, but in a life-enhancing way. The liberal, by contrast, starts his day with the blame game: "I was bullied, people were mean to me, blah, blah, people suck, I'm a victim, I need a government program to stop me from mainlining heroin, blah, blah, et cetera ad nauseam. A caricature? Of course. But it lays bare some important home truths like all good caricatures do.
Perhaps we could say that the right-thinking person begins with a defeasible presumption in favor of his ability to rely on himself, to cope, to negotiate life's twists and turns, to get his head together, to be happy, to flourish. He thus places the burden of proof on the people and things outside him to defeat the presumption. Sometimes life defeats our presumption of well-being; but if we start with the presumption of ill-being, then we defeat ourselves.
We should presume ourselves to be successful in our pursuit of happiness until proven wrong.
6. Rely on yourself for your well-being as far as possible. Learn to cultivate the soil of solitude. Happy solitude is the sole beatitude. O beata solitudo, sola beatitudo. An exaggeration to be sure, but justifed by the truth it contains. In the end, the individual is responsible for his happiness.
7. Practice mental self-control as difficult as it is.
8. Practice being grateful. Gratitude drives out resentment. The attitude of gratitude conduces to beatitude.
9. Limit comparisons with others. Comparisons breeds envy. The envious do not achieve well-being. Be yourself. Hike your own hike.