Appy

Relax. Lighten up and don't take yourself too seriously. Stress can cause many mental, physical and spiritual problems in your life. One of the major causes of stress is worrying about things that are out of your control. If you find yourself constantly worrying about things, assess their condition or cause and whether you yourself can do anything to improve the situation. If you can, work on it. If you can't, learn to recognize that these situations are simply out of your power and control should be out of your mind as well! Work on being able to laugh at things, especially yourself. If you make mistakes, learn from them, work around them, and move on. Set aside time each day for you to reflect on the day's events and simply have some "you" time.
Smile. You would be surprised how much of an immediate physical difference smiling has on your mood. If you smile and force a little laugh, you will feel your mood lighten, and you won't have to force it next time. Laughter is a powerful, positive medicine. The calmer and more peaceful you feel, the happier your life will be. Accept the situation, whatever it may be, and lighten up with a grin.
Take the good with the bad. No one is happy all of the time. We cannot change the past, but we can enjoy the present, and look positively to the future. Obstacles will always be in our way, holding us back and knocking us down - it's a part of life. Realize this and avoid becoming down or starting to think too negatively about your situation. Good and bad wouldn't exist and be in balance without each other. Each one teaches us our fair share of life's lessons. Take as much as you can from events, whether they left you feeling joyful, accomplished, angry, confused, or sad. Treat each obstacle as a learning device and each knockback as a toughening of your character. Learn to accept that things aren't going to be perfect all the time. In completing this, you will find your days much easier to get through.
Be thankful. It may sound cliché and overused, but learn to be grateful for what you have, rather than what you don't. If all you ever think about is how you can't afford the things you want, how you're not "popular", how you're not "attractive" enough or no good at anything, your life will become less and less enjoyable before your eyes and all at your own doing. Changing the way you think about things and the view you take on your life can have a big impact on you as a person. Looking around you, carefully realize how lucky you are to have the things you do, whether it be a loving family, great friends, an amazing job or simply a roof over your head. Remind yourself of why you are fortunate to be living the life you do, and focus on making the most of the gifts you have been given. Everyone in this world has something to be thankful for, and realizing that can lighten up your way of looking at life entirely.
Be yourself. Much criticism is caused by people who are discontented with themselves, not with you. Your goal may be to open up completely to yourself and learn to be your own best friend by being completely honest with yourself. What do you want out of life? What makes you truly happy? Who do you want to be? Don't hold yourself back or fake things to become well-liked, or because you're too afraid to be who you really are. You owe it to yourself to do one thing: Be you!
Pursue goals that make you happy. Strive for long term goals rather than short term satisfaction. It's very easy to gain short term satisfaction - a quick high, a fast relief from your current problems (such as being angry, smoking, lowering self esteem etc.). But it is what it is, a "short term" satisfaction and the effects die out very soon, leaving you with an empty feeling that is sometimes worse than before. Set long term goals, goals which take time, thought and effort to achieve. This will make you continually work towards improving yourself and will give you the satisfaction of bringing a permanent change in your life.
Focus on the objective. If the thoughts you are thinking are not giving you that 'good feeling', then think about something else that will make you feel good in that moment. Observe your thoughts and ideas consistently throughout the day. Sometimes this may not be as easy as you think if you are stuck in a "destructive" train of thought and your brain chemicals are getting fired up and forming "anxiety or anger" thoughts. Anxiety, fear and anger patterns can be interrupted by focusing on something else. This will dissipate the rush of chemicals that are making you feel bad. Immediately then go back to picturing scenes/remembering things/imagining, planning stuff that makes you feel good.
Develop healthy relationships.
Have a healthy relationship. If you're dating, get involved with activities that reflect who you are, and get to know people who like the things you do. Get involved with someone who loves life and pursues happiness the way you do. If you're in a relationship, strive to make that relationship healthy.
Choose your friends carefully. Nearly everyone needs someone who cares for them and treats them well. If you have friends who are treating you badly, or are not supportive of you and your goals to improve your life, then find friends that do care about you. If you can't find any friends like that in your current circumstances, then look elsewhere. If you're feeling sad, there's nothing like going out with your friends to make you feel better. Surround yourself with friends who are beneficial, encouraging, and helpful. We all need this continuing, nurturing encouragement to make solid desired progress in life. We also need friends that will lovingly tell us the truth to help us become better people(even when it hurts), not friends that will instead criticize us behind our back.
Maintain your relationship by keeping in touch, making an effort and enjoying your time with whoever the person is. Support each other through hard times, rejoice in the good moments and together be thankful for the friendship and love you share.
Diversify and Balance. Studies show that the happiest people often have several things going on in their lives at once and they learn how to balance them. They have a career, a relationship, a hobby, social activities, an exercise routine. They volunteer, meditate, learn new things, etc. So, if one area of life goes awry, there are still plenty of other areas to help them cope and that are still going well!
Make someone else happy. When you're feeling powerless to create happiness in your life, do something to make someone else - anyone - happy and you'll remember how easy it really can be. Isn't it true the happiest people we know are typically the ones, who for some foolish reason, are always ready to give you the clothes off their back? And frequently it is true that the most discontented people are the ones who are selfish, demanding, and inconsiderate of others. The happiest days of our lives, when we really dig down deep, are the days when we see a smile on the face of a person who we care about. Even helping a stranger can remind you of how much you really have, because of how much you can give.
Dance, sing and laugh as much as possible, for every reason and for no reason. If you don't feel like it, put on some music that you know will make you feel like it, or watch or read something that makes you laugh.
Forgive and Forget. Don't allow yourself to be overcome by anger, sorrow, wrath, or life. When you release others and let them go, you release yourself to live life to the fullest as well. Accept people's apologies, even when they are not packaged exactly the way you hoped. Move on. Forgive yourself too. Nobody is perfect, we all make mistakes. Learn from your mistakes and move on.
Get a partner! It's great to be with someone!