Counter whenever you can, if you're trying to get a certain hit count (10, 20, 40) then use the special take-down maneuvers for far away enemies and use the freeflow combat as a way to dodge and attack enemies. Also remember to tap X or A whenever you can to go over an enemy if you want to get the Freeflow perfection achievement/trophy, you'll need to use this perfectly. Also remember, unless you're going for freeflow perfection never use the finish move, let the enemies get back up.

If you do that it'll leave you open for an easy attack. Only use this when it's the last enemy, you have room to work with, or all other enemies are knocked out. And finally just remember to use the batclaw/combat batarang when you are in a pinch. It'll take down enemies to give you time to get yourself together and continue a perfectly executed brawl. Do as this guide says and you should be able to get these trophy/achievements as well as dealing multiple enemies without taking damage.