After those areas have been taken care of, begin matching tiles at the bottom. The falling blocks might remove a lot if new matches are made.
Give priority to tiles that cannot be placed in a match. Focus on removing them all as soon as possible.
If your goal requires clearing a lot of mud or goo and removing a reptile, concentrate on clearing obstacles first. A reptile will probably end up in your path as you are cleaning up.
Start with the hard to reach places, especially in later levels. After those areas have been taken care of, begin matching tiles at the bottom. The falling blocks might remove a lot if new matches are made.