Infuse your praise song with heavier drums that place the emphasis on the first and third beats. Rock 'n' roll music is characterized by driving rhythms and beats, so having a louder rhythm component will give your sound a bit more energy.
Replace acoustic guitars with electric guitars. Rock 'n' roll developed from rhythm and blues, which often used electric and distorted guitars. If you don't have electric guitars, consider buying a guitar effects pedal to give you the electric sound.
Consider speeding up the tempo of your praise song. You want the song to elicit the same response as a rock song, so you should infuse your sound with liveliness by speeding it up a bit.
Make sure the words can still be heard. This is crucial to maintaining your message and avoiding the perceived decadence of rock 'n' roll that many churches condemn. If the vocals are not loud enough, you should consider having multiple people sing the same part.
Add theatrics to your song when you perform it. You don't want to do anything sacrilegious, but you can do things that augment the message of the song, such as having a religious slide show, bringing people on stage to sing or adorning the stage with religious imagery. You can even end the song by reading a Bible verse over the sound of strumming guitar chords.