It DOES take some practice to figure out to attack a base so as to take down their TH.
They are all different, and your troops, also have, um, a mind of their own.
There are some things that tend to help. If you click their castle, you can see at least how many troops are in it, and, the circle that activates them to come OUT and fight.
Same with any royals or towers, etc....you can see their range as a circle around them...so, you want to ideally, for example, have your archers take out stuff from just outside the D's range, etc.
If you lure the castle troops out of the base, and kill them all before continuing, it avoids them hacking YOUR guys up IN the base.
If you look at a base and it seems there are gaps that probably have traps, etc...send 1 low value troop in to blow it, not ALL your giants, etc.
Look at what D is covering the TH, and if there's a place you could be that allows you to kill the TH, but NOT be in range of their D, that's a good spot to try to get to. If taking out some KEY D would make that work, then, plan on taking out the covering fire first, THEN move troops to the take down. Giants for example go after D specifically, but archers and barbs for example will make you crazy attacking builders huts, while the enemy is shooting at THEM. The giant will IGNORE their TH until ALL the D is gone, so, giants can make a path free of cover fire, but, you need to follow them in like troops behind an infantry tank, etc...with troops that WILL attack non-D targets.
The early bases have the least air defenses, towers mostly, or low level AD, etc...archers or wiz in their castle, etc. If you can get a maxed dragon in YOUR castle for example, and release it after your troops taken out the base's AD, that thing will eat the entire base typically all by itself. Even borrowing a castle full of minions will quickly overwhelm the typically canon/mortar based D's....just make sure the archers and wiz towers are neutralized first.
If you drop a spell, aim of the lightening is critical...and for the others, make sure you put the circle so it covers everything you want attacked, not dropped ON your attackers on their WAY TO the area of interest.
And so forth.