Writing Tips: Worldbuilding

This is a part of writing I don't often see covered, but it's an important point: a lot more important than some people think. Worldbuilding is a lot more than being able to fit your imaginary country on a map or make a globe with your continents on it. It's figuring out the whys, wherefores, if-thens, and what-ifs that make your world more than a backdrop for the story.
One of the things I've always found important is nailing the climate and the clothing that goes with it. Let's be realistic, here: if your land has bone-chilling winds regularly whipping off the arctic ice that sits only twenty miles to the north, your characters will not, repeat not be walking around with bare chests, short sleeves, or in light fabrics. Clothing materials that will make sense are wool, leather, and lots of fur, with little to no bare skin exposed to freeze. Conversely, if your characters must move for some reason from biting cold up north to the blistering heat of a southern desert, do not expect me (who lives in the Texas Panhandle and thus right on the edge of the Great American Desert) to calmly expect that these cold-tough but heat-wimp heroes will be able to travel through the murderous temperatures without ditching a considerable amount of clothing, and fast. Equally, I can see a beauteous princess who comes from a jungle setting being perfectly comfortable in a nudist society. I can't imagine someone from the temperate (read: chilly) regions of northern Europe being so.
Second--and this I have found rarely detailed--is the way the flora and fauna of the area dictate the lives of the characters. Emily Rodda's Rowan of Rin series does a great job of detailing how the ecology of her various lands works, and the marvelous Edge Chronicles do such a great job of making a completely alien world look realistic you almost expect to find it on a map. But most other stories ignore this altogether. Yet this used to be such an important part of life that I find it weird that we forget about it! The flora and fauna in a region dictates what your people eat, how they live, what they fear, and sometimes what their transportation is and how they make war on each other. In a desert region, for example, they will subsist on what grows around the oasis, what they can hunt, and what their herds of goats and camels can provide them with. In the jungle, they have fruit, meat, and vegetables in plenty; the real problem is keeping the wild animals out of their crops and their villages. You don't have to go into pages detailing how the lives of your character intersect with the world around them; but if you put in hints that help us understand how their world works, it really makes the story come alive.
And finally, something I have almost never seen done is how the terrain looks or appears to an outsider. This is probably something I notice more than most people. I come from the Texas Panhandle, and often see people from other places react with shock to certain things I take for granted--for instance, the nearly non-stop winds and cacti waiting in ambush. On the other hand, when I went to Colorado and tried to hike in the Rockies, the thin air just about did me in--and in Washington State, I always like to go in the autumn, when the blackberries are ripe and I can go pick them. If your characters enter a region with topographical differences, they will notice--and making them notice can be a lot of fun.