Psalm 150 is a powerful call to praise God with everything we have and in every way we can. Verse 3, specifically, focuses on using musical instruments to express that praise:

"Praise him with the sounding of the trumpet!" The trumpet was a loud, fanfare-like instrument often used to announce important events or victories. Using it to praise God signifies celebrating God's glory with boldness, fanfare, and exuberance.
"Praise him with harp and lyre!" The harp and lyre were stringed instruments often associated with melody, beauty, and skillful music. They represent a more refined and delicate expression of praise, emphasizing the beauty and artistry in worship.

In essence, the verse means:

Use a variety of instruments to praise God: This isn't just about the specific instruments mentioned. It's about using the musical talents and resources we have available to express our worship.
Praise God with all kinds of expressions: The contrast between the loud trumpet and the gentler harp/lyre suggests praising God with both bold, joyful celebration and more contemplative, beautiful expressions.
Offer skillful and intentional praise: It implies that we should put effort and artistry into our worship, rather than just going through the motions.

More broadly, the verse contributes to the overall message of Psalm 150, which is:

Praise God with everything: The whole psalm lists various instruments and activities, signifying that every aspect of our lives should be dedicated to praising God.
Praise God everywhere: Psalm 150 ends by stating "Let everything that has breath praise the Lord." This emphasizes the universality of praise - everyone, everywhere, should praise God.
Praise God for who He is: While not explicitly stated, the implication is that we praise God for his goodness, power, and glory.

In conclusion, Psalm 150:3 is a call to use music – both bold and beautiful – to express our heartfelt worship and appreciation for God.