Basically the approach is to use it for the boss fight and go and smack-down four monsters between every attack. On normal-difficulty dungeons it's possible to keep a train going by fighting monsters like goats or gorgons, but in hard and vicious (ie, the dungeons where you need that attack bonus) that's just not practical. This is an ability that works better on paper than in reality. It's not bad, but if you were expecting to repeatedly chain +100% damage attacks you're in for a disappointment.
Remember that attack bonus multiplies your base attack, so this ability is amplified by anything that improves your base attack. Trisword, Orcs, the Fine Sword, all are superb for a Crusader. In fact, there's really no reason to play a Crusader as any race except Orc.
Don't overlook the Crusader's other two class features. Scarred is very powerful, particularly in dungeons that feature weakening. The catch is you need to suffer the debuff first, which is nasty at level 1. Carry a fortitude potion to cure it. On most dungeons, you'll want to seek out the nearest mana burn monster to gain that immunity. It's rare that you'll want poison or corrosion immunity. You cannot gain immunity to resist down.
Of course, the extra altar granted to the Crusader is a nice perk. With the extra altar prep he can have up to five altars, which is a whole lot of deities to work with. Your chances of finding a specific combo are actually very good with a crusader.
Overall, though, the Crusader only shines on the Ick Swamp scenario, where weakening is pretty much unavoidable and melee classes need to prep a really big sword. Outside of that level, there just isn't enough weakening present to leverage an advantage from his "scarred" class feature and the other two bonuses he has going for him aren't enough to carry the class.