Spend time with those you love

This is an easy way to get endorphins streaming throughout your brain, because when you feel connection, you feel peace, joy, and safe
The time you have to do this of course may vary for each individual, but making an effort to spend time with someone for even a short time will help

Spending time alone doing something that is a passion

I know this goes against the first tip, yet honestly it can be just as important to recharge your batteries and happiness mojo if you practice hobbies/passions that are yours
Taking time to reflect and sort out your thoughts will decrease your drive to perform around others and allow to connect with your inner life

Spend some extra time to sleep

Research suggests that a huge mental cost occurs when you don't getting enough sleep
In addition research also suggests that those that sleep less tend to have experience more repetitive negative thoughts

Eating a balanced diet

There is science around eating certain foods and having that lead to a "happiness" neurotransmitters: Eating foods that are high in protein and specifically have a higher percentage of tryptophan (like turkey, sunflower seeds and pumpkin seeds), will provide much needed tryptophan, the precursor to serotonin. Serotonin is the neurotransmitters that medications such as Prozac is attempting to rebalance in the brain.
Having a healthy gut, can provide relief as well, so if you experience GI issues, consult a doctor/nutritionist to see if changes in your diet are necessary

Spend time outside

Early morning sunlight is more intense and this can boost your body’s production of melatonin in the evening. Serotonin converts to melatonin for a great night’s sleep.
Getting outside for a 20-minute walk in the early morning sunlight can boost your mood and improve your sleep!
Plus fresh air, and exercise can promote endorphins in the brain as well