The first thing is to realize that joy is a gift from God. The root of the word joy in the Greek is chara, which is closely related to the Greek charis for "grace." Joy is both a gift from God and a response to God's gifts.
Following God's command to be joyful in the midst of trials is really a matter of perspective. If you really look and think hard enough, you will always find something to be grateful for, even if life seems too hard to follow. Be grateful for your relationship with God, grateful for your health, grateful for another day of life. Be grateful that your situation is not worse than it is. If you go back, you can find the joy and encouragement that God is sending you. Be grateful for something as simple as a bird that suddenly flew and made you smile. With this in mind, it is evident that one way to experience joy is to focus on God. I say this from my own experience, if I spent all the sad days due to adverse situations my life was a chaos, when I look back and see that my attitude is the one that determines the test, then those tests are like waters that passed, I have scars but not wounds because the power of God operates in my life.

One day God told me: you need to be tested, it is the only way I show you my power and manifest my glory in your life.