So many bases waste their bombs. So here is my guide. I'm a former world no1 defence only player... So kinda worth trying my tips :)
First, to win you want your bombs triggered often, and as early in the attack as possible. This means mostly bombs in the second layer of defence (cus bombs MUST be between defence buildings and also double as wallbreaker defence). If they in the middle you've probably lost the defence by the time they get used.
Second, bombs are critical hog defence, which means they always go between defence buildings. Spring traps get placed between def buildings one between each cus one will spring three hogs but two together wont do 6 hogs - so better to place one each between two defence buildings. Also big bombs are great between defence and next to wiz towers. Big bomb hurts a bunch and with no heal the wiz tower splash damage might even kill a full hog bunch.
Third, bombs need to be deployed with dual purpose. Put them against walls as well as between defence so that they double as wallbreaker defence. For small bombs if maxed use two together - a pair of small bombs does enough damage to kill max wallbreakers.
Next is air bombs - black air bombs hit a single target so they are best deployed on the perimiter (so they kill attack early before the attack does too much damage) in the weakest air defence part of your base.
Finally the all important red air bombs - they do splash damage and 2-3 together can kill a balloon bunch... So i use em to protect my townhall or my infernos - 2-3 together to kill a bunch - ballons often bunched by the time they get to middle.
Finally, if u can manage it big bombs are also great witch and wizard defence so if you can place next to a wizard tower in the middle of a big pocket u can often kill a bunch of wizards or witches.
Check out my bases for examples.
Predator, MEGACARNAGE (author predatorclash)