I've loved gnolls since I first picked up the game, but I've never used them as written — I got as far as the "hyena-people who treat their females as chattel" and suffered a fatal disconnect. So instead they became a faintly savage, matriarchal group of clans, the brutal pragmatists without actually being full-bore evil.
Among the tricks I've used:
- Strong ties to natural magic. Gnolls might not have much by way of wizards, but they have some very dangerous druids. Shifting, calling down natural cataclysms, the whole nine yards.
- Assuming a hyena-ish anatomy with a long torso and long arms (and high Strength), they would probably favor weapons that take advantage of that leverage: axes, hammers and flails. Gnollish longbows are built for a powerful, seven-foot archer with disproportionate arms, and would be hard for a human to use; they have a base damage of 1d10.
- Man-eaters. Gnolls will eat any humanoid they catch and kill, as well as other animals. Some clans hunt ogres as if they were hunting large, dangerous prey like Cape buffalo. It's always fun to have players find gnoll-made trade goods like minotaur-horn vessels, trollbone chariots or ogre-skin leather.
- Cunning. I once stymied my players by having some gnolls just hang up a sheet across a defensible entry into a ruined city wall. The players wound up going the long way around, reasoning that the gnolls were probably up to something they didn't feel like dealing with.
- Hyena motifs. Here I pulled out the strong matriarchal influence, but also little touches like them being effective and brutal killers as well as scavengers; not the biggest beastie on the block, but among the most dangerous. They'll pack up and move rather than get into a fight that might exterminate the whole clan, but if they need to fight, it's no-holds-barred.