Tip #8 is a given but it's really interesting how much we think about doing this but never get around to it. Pray. Talk to God about our lack of joy. The Psalms show us that David poured out his heart to God, revealing deep emotions that almost seem irreverent. But he wasn't being irreverent - he was being transparent with a honesty that God alone can deal with. Apparently, King David knew that he needed to get the negative emotions out before they could be replaced with positive ones.
So, talk to God. Then listen to what He has to say.
Tip # 8 -- Pray.
Tip # 9 involves talking, too. Talking to yourself. I know that sounds crazy but hear me out.
Psalm 42:5, 6 records the conversation David has with his soul...and the answer he gives himself.
Why are you cast down, O my soul,
and why are you in turmoil within me?
Hope in God; for I shall again praise him,
my salvation and my God.
I find it very beneficial to monitor my self-talk --- instead of letting my soul speak lies and negative thoughts, I tell myself to instead listen to the truth. It's amazing how much of our thought life is not based on the truth. We fall prey to vain imaginations ("I'll bet so&so said/did/thought such&such about me" or "What if _________ happens? What will I do then??") and false assumptions ("He will never change" or "I can't do this anymore") and outright lies ("I am hopeless" or the equally destructive opposite "I am right" and "Nobody understands what I'm going through") Lies that steal our peace and joy. Instead of Truth. And that Truth gets me back to tip #7 -- God's Word.
When the blues threaten to overtake you, try having a self-conversation like David did. Ask yourself "why are you so sad? why are you so stressed?" Then, give yourself the answer of TRUTH before the voice of despair can respond - "My hope is in God. He is my joy and my salvation. I shall praise Him." "I can do all things through Christ who strengthens me" "God's love is from everlasting to everlasting. He will never leave me or forsake me". " ALL His ways are loving and faithful". His plans for me are good, plans to prosper me, to give me a future and a hope". "My heart is deceitful so I cannot trust it - instead I will trust in the Lord".
Tip #9 - Speak TRUTH to yourself.