There are several ways to go with Gnolls.
On the one hand, they could be the degenerate 'dog-warriors' of a long-lost Egyptian-style kingdom, and have sleeker jackal-looking heads, more like depictions of Anubis. Over the hundreds, or perhaps thousands, of years since their empire fell, they have become savages who hunt in packs among the mummy-infested ruins of their once-great kingdom. They would still be adorned in Egyptian-style gold and lapis jewelry, pectorals, headresses, etc. and their shamen might retain some knowledge of their former glory, and occasionally have some ancient relic looted from their earlier days. They could also be dead wrong, and their species have been the slaves of the culture that built those ancient cities, but due to the destruction of any art depicting hawk-headed or bull-headed or cat-headed gods and goddesses, they are convinced that *they* built these ancient ruins and that they are the ones who will someday reclaim the glory that was 'stolen' from them!
On the other hand, the core presentation of Gnolls has Ranger as their favored class (instead of say, Barbarian, like the Orcs), and seems to have made them a more nomadic race. Anything but lazy, since they spend their entire lives on the move! In this case, reading up on hyenas and current quasi-nomadic cultures can provide the basics to fashion a Gnoll culture that follows great herds of wildebeest or other cattle-like creatures (zebras, water buffalos, bison, caribou, whatever fits the area of the world you want to use) and both protect the herds from other predators, and, naturally, prey upon them exclusively. Such a culture would be likely to have domesticated hyena packs and perhaps even dire hyenas, in the same way that human nomads would use dogs or horses. They would have strict heirarchies, and if similar to hyenas, the females would be larger and in-charge (and most likely to be the beast-tamers who have packs of hyenas or even dire hyenas under their control), with the males relegated to lower status. Being that their favored class is a spellcasting class that derives it's powers from it's connection to nature, the Gnolls would be *very* unlikely to be complete savages, overhunting or despoiling their territory. They might be completely savage to anyone who shows up in their territory uninvited, but their lands would be ruthlessly well-maintained, and they would likely choose overpopulated animals or invader species as their prey of choice, so that the herds they depend upon don't suffer from displacement or disease. This wouldn't in any way make them 'good guys,' and they would be just as likely to run down and massacre anyone they consider 'intruders,' and, since the herds they follow are migratory, their 'territory' might change from season to season, as the herd moves into more developed lands. The Gnolls wouldn't care one way or another if humans set up a village here a decade ago, it's always been their land, and this is the way the herd is going this year. The humans 'intruders' are gonna die, especially if one of them does the unthinkable and poaches from the herd that the Gnolls consider their property...
These sorts of concepts can be combined together. At one end of the great plains, tribes of gnolls follow herds of beasts. New packs try to find or even *create* their own herds, capturing livestock and trying to get them to adopt a nomadic lifestype (a horrible idea that ends up with them raiding human farms and chasing milk cows until they drop over from exhaustion, since Bessie is anything but a 'herd animal' by this point!). Other packs lose their herds, or individual Gnolls get cast out of their own packs by their alpha females for this infraction or that disrespect, and they form into bandits and thugs, raiding other races (but rarely their own kind, because they can't compete with the organized Gnollish tribes) and farms and whatever, becoming more Orc-like in behaviors. At the far end of the great plains are the gnolls who skulk among the ruins, who believe that all Gnolls have a birthright to restore the great empire of the sands. The matriarchs of the middle plains call them fools, pointing to their own nomadic herding societies as all the 'birthright' any Gnoll would ever need. They might occasionally fight amongst themselves, the 'Egyptian' Gnolls convinced that they have to unite the nomadic tribes and 'convince' them, by conquest, to reform the kingdom. Charismatic warlords among these attempt to beat smaller tribes into submission, and who knows, perhaps someday they will succeed in gathering the plains packs together in service to their mad quest. Then again, the nomadic matriarchs might be willing to put aside their own squabbles and territorial disputes to stand against the 'mad ones.' Gnollish civil war, in the shadows of the pyramids!