There are two strategies for this level and Strategy #2 gives you higher score.
Fire the Yellow Bird to pop the two pigs on the two far-right horse. Then, use the Boomerang Bird to explode the TNT and pop the Small Pig and the Moustache Pig. Next, shoot the White Bird and drop the egg bomb between the Helmet Pig's horse and the Medium Pig's horse if the Helmet Pig is not being popped yet or drop the egg bomb on the Medium Pig's horse if the Helmet Pig has been popped.
Shoot the Yellow Bird to the TNT and pop the Small Pig and the Moustache Pig. Sometimes, the Medium Pig's hat will start to roll slowly to the right and pop himself and the Small Pig below. Then, shoot the Boomerang Bird and boomerang him to the Helmet Pig. Third, shoot the White Bird and drop the egg bomb between the two far-right horses to clear the level.