Most of our top TH8 hoggers have had lots of experience and plan out their attack very carefully. A Tesla or multiple springs can cause your hogs to divert from a plan and you have to adjust on the spot. Pre-planning your first heals is also an important factor, make sure they stayed healed through 2x4 areas (double giant bombs) and near Wiz towers (xbows for TH9). Another threat most new hoggers ignore is point defenses. They will dwindle the hp of your hogs very quickly if not planned properly.
The JTJ clan has written up a very extensive guide on how hog pathing works and what goes into your attack plan when scouting. If you are TH8 and want to move up to Hogs, take some time to read this guide.
https://jtjclan.wordpress.com/2015/05/16/th8-scouting-and-planning-hog-attacks-during-clan-war/
Their terminology is slightly different and a little more complex than ours so I advise to use this page if you are confused with the lingo...
https://jtjclan.wordpress.com/slang/