Dr. Weil's personal opinion is that the neutral position on the mood spectrum - what he calls emotional sea level - is not happiness but rather contentment.
The simplest breathing practice is just to observe the breath, nothing other than that. Just to keep the attention on the breath cycle without trying to influencing it.
Deficiencies of vitamins and trace minerals have been reported in people with mood disorders, and these days, deficiencies are widespread.
An anti-inflammatory diet & lifestyle can be effective both as a treatment for and a way to prevent depression. Try the Watermelon & Heirloom Tomato Salad.
Human bodies are designed for regular physical activity. Regular physical exercise can help prevent depression and maintain a balanced mood.