Detonating TNT is the key for 3 stars but making the second shot harder. But three stars is not hard.
One strategy for Pig Bang level 1-29 is to send the first Lazer Bird into the bottom-right TNT along a straight line. It is a good spot, and has the potential to detonate all cornered TNT. Use the next Lazer Bird to go through the center pig and into the TNT on the extreme right.