I have felt that way before, somewhat recently, actually.
How often are you in His Word? How often do you pray? It's not that there is a checklist of "Do this or do that and you will feel better", but I have found that doing those two things often helps. If you're not sure where to start in the Bible, maybe check out a study (interactive ones with questions help you dive deep and examine yourself at the same time) or go through a book. Be honest with God, and ask Him to give you that passion to want to read and learn more about Him. Perhaps ask Christian friends or family members to pray for you and with you.
Pray. Praying doesn't just have to be that one specific time where you close your eyes and are in a quiet place. Praying, to me, is communication with God, and that can be when I see a pretty sunset, and I think/pray, "Wow, God, you're an awesome Creator!" or it could be when someone is rude to me and I pray, "I am so irritated right now. What's his deal? Lord, help me see things through Your eyes." Etc.
There isn't really a formula, but hopefully those things will be a start!