Psalm 111:1 Praise the Lord! I will praise the Lord with my whole heart, in the assembly of the upright and in the congregation.
When you study the rest of the above psalm you will see that you are to praise Him for His faithfulness and justice. Praise Him with your whole heart.
The more you sincerely praise the Lord, the more you will find that God will give you something to praise Him about. Many Christians limit their praising the Lord to the times when they have something to be joyful about.
They hurt themselves by doing this because they limit the power of God from flowing through themselves. There will be times when you do not feel like praising the Lord. It then becomes necessary to spend time giving a sacrifice of praise to God.
The more you study His Word, the more you will find things to praise the Lord for. Make a real effort to become better acquainted with the Lord through praise.