Happiness and joy are a choice. You can choose to be happy about your life, or you can choose not to. Also remember the verse, “The joy of the Lord is your strength. " If you want to have strength for your life, choose to have a subdued joy and contentment no matter what.
Paul said, “I know what it is to be in need, and I know what it is to have plenty. I have learned the secret of being content in any and every situation, whether well fed or hungry, whether living in plenty or in want. " Even Paul had to learn how to be content. No one is born innately knowing how to always be content, but we can learn how. Another great verse is “godliness with contentment is great gain. " If you can learn to praise God for your life as it is now, rather than always wishing that it were different, you will be much less likely to complain about things.
Consider, “Whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable—if anything is excellent or praiseworthy—think about such things. " (Philippians 4:8). If you think only about what is true, noble, right, pure, lovely, admirable, excellent and praiseworthy, you will have no room in your thoughts to think about what is false, wrong, impure, ugly, or not admirable. Write some positive thoughts you can think as alternatives to complaints, and keep the list handy.
See the humble reality of who you are rather than thinking you are someone greater than you are. Humbly say, “You do not even know what will happen tomorrow. What is your life? You are a mist that appears for a little while and then vanishes. " (James 4:14). The reality is that our lives are very fragile and finite. We really can’t even expect for sure to be alive tomorrow, let alone that tomorrow will be our best day ever. Accept that you don’t have control over everything, and remind yourself to only focus on what you do have control over.