There is an old saying "fake it till you make it". This goes double for world building. You don't actually have to have a fully detailed world all mapped out and meticulously recorded for it to seem like you do. All you need is mastery of two techniques.
The first is record keeping. Everytime you add a detail to your world or even just have a flash of inspiration, write it down. Any kind of notebook, card file, or what have you will do. Just be sure and write down what you came up with so you can refer to it later. Over time these random jottings will accumulate into a fully fledged world.
The "world map" can be as simple as a large blank sheet of paper with the names of major geographical features jotted down in their relative positions until you fill in what else is there. Just being able to see that the Boiling Sea is south of the Avacado Jungle of Death can help you decide where the Cold Wastes should *not* go. (Hint: they would be unlikely candidates for southeast of the AJD)
Record keeping also allows you to have recurring themes. If you establish a group of raiding bandits in one adventure as the "Riders of the Red Hand" your world will grow more depth if the next time the players hear rumors of nefarious activity it is also attributed to agents of the Red Hand. (NB: you do not have to establish at this point who or what the Red Hand is. Simple repetition of the name will give the world depth and resonance.)
The second technique to practice is broad stroke improvised description.
A colourful, ineresting name, such as "Riders of the Red Hand", will set the players imaginations to wondering who or what the Red Hand is. Much more interesting than just "you are attacked by a bunch of wandering bandits". Keep notes of what your players guess or speculate. It may or may not prove to be correct, but it is always a rich source for later inspiration.
Keep mental tabs on interesting bits of news, pictures, etc. They can often be recycled for game use. A current news example is the ice floe that broke off in Lake Erie carrying away about a hundred ice fishermen with it. This presents the germ of an idea of a large piece of land/ice/flying castle drifting off with the players (or their goal) on it. Will it break up before they complete their mission/escape/rescue? Why did it break off in the first place? Lots of possible adventure seeds.
National Geographic or other magazines that give one or two word summaries of the articles inside can also be a great idea generator. Just look at the subjects and try to think of some way to tie them together. A glance at today's Yahoo headlines gives huge wildfires in Australia, China diverting rivers to combat drought, and huge numbers fleeing a Sri Lankan warzone. Tying these together gives a huge population of refugees fleeing a war between two wizards. One wizard is a master of fire and is sending flame elemantals to devastate his rival's kingdom. The defending wizard is diverting rivers from their beds to combat the fire elementals. The players could be siding with eiother wizard, or just caught in the middle.
Or perhaps the story above is ancient history or local legend, and the adventure is a quest to find some powerful artefact left over from the now ancient conflict? I don't know, I just picked the headlines and made up the story while I was typing.
Making different Kindreds have unique cultures is just as easy. Pick an interesting culture (or even just an interesting practice) and give it to one of the Trollworld Kindred. My lizardman at left is based on a photo of a Maori warrior and a marine iguana. Adding these two together gives us lizardmen who are culturally similar to Pacific islanders, catamarans, tebutjes, headhunting, and are also vegetarian (iguanas are herbavores) they likely are in demand as sailors and perhaps are skilled navigators. Instant unique lizardmen. No longer crocodile or aligator like swamp dwellers.
For centaurs, how about combining plains Indian culture from the Old West with knights of high chivalry? Armoured fighters who contest with lances to score the first touch (or the first fall) then seek another opponent. Proud, haughty and independant. Living in mobile tent cities, raiding other tribes and engaging in very formalized mutually agreed upon wars. Vey different from their classical Greek origins, yet it still works.
What about the Aztecs? Feather bedecked jaguar and eagle knights, pyramids and bloody sacrifices. Perhaps Urooks? Or a tribe of bloodthirty Hobbs?
A long as you can come up with a vivid image or two on the spot, and something that hints at deeper levels no-one will know that you don't have the whole world built in detail.
JRR Tolkien admits in the preface to Lord of the Rings that "the tale grew in the telling". In the Hobbit, the Necromancer, the elf-goblin wars, Gondolin and even the Ring itself were not fully developed in Tolkien's thought. It was only with time that they became the threads that wove the Hobbit into the tapestry of Middle Earth.