I've gotten the basics of Blender down, and I have finished my first model! However, I'm now stuck trying to figure out how I'm going to turn my model into a set of functioning sprites!
What process did you go through to get your Blender creations in the game? Do you have any tips or tricks for people wanting to make multiple sprites from the same model? What kind of lighting do you use?
First of all, congrats on your first model!
Spriting is not usually difficult--especially if you have a program like Photoshop or Gimp which you can use to edit your sprites. However, you've asked a lot of good questions, so I'm going to write you a bit of a novel.
The first thing to be aware of is the fact that pure black will be transparent in Creatures; you can try making your object's textures Emit just a little (a trick Moe taught me) so that its shadows will never be pure black, or you can adjust the lighting in another program after you render. The end results are the same, but the Emit method takes less time.
The second thing to be aware of is the way Blender handles blurring (called anti-aliasing). The scene settings screen includes options to change anti-alias settings; you can turn it off completely by unchecking the "oversampling" button. You may also want to experiment with what kind of anti-aliasing is applied (in my version, the drop-down box is located beneath the oversampling button). The default is Gaussian, but I like CatRom better because it preserves more detail.
Once you've adjusted the camera position and dimensions, and anything else you might want to fine tune, hit the "Render" button or hit F12 to render. Blender does have settings to let you save a rendered image in BMP, PNG, etc. format. I know Moe developed a method for batch processing the render-save process, but I'm not very savvy about batch processing. I usually just cheat and print-screen the finished render, then paste it into Photoshop.
Theoretically, you can completely skip the need for further processing by making your object Emit a little, turning anti-aliasing off, and making the background black.
My favorite method is to render the sprite itself with oversampling turned on, so the details will look nice and pretty. Then I render a second version with oversampling switched off. That way I end up with both a "pretty" sprite with smooth details, and an exact outline I can use to cut out the background in Photoshop.
For multiple sprites:
If we're talking about something that could conceivably have joints (an animal, a robot, a tree with swaying branches, etc.), it's best to give it a skeleton and create an animation. (I learned the basics from Blender 3D: Noob to Pro.)
If it's something that can't have a skeleton, but undergoes some basic transformation like getting bigger (a growing plant) or turning at an angle (a rolling ball), animations are good for that kind of thing too. Blender animations let you "tween" an object, so you only need to specify the number of frames, and the beginning and end settings, and it will calculate the settings for the frames in-between for you.
If it's something so drastic that you really need to use multiple models, an easy way to handle that kind of scenario is to put each duplicate on a different layer in the same file. (In my version of Blender, the layers appear as a grid of white squares just below the camera window.) Hit 'M' and pick a square to move an object to a different layer.
The same object can be placed on more than one layer if you like (hold down Shift to select multiple squares), so you can have a machine with some stationary parts, include the same lamps on all layers for consistent lighting, etc. Only the objects/lamps on the layer you're currently viewing will be rendered, so it's a lot like having multiple files in one--except lighting and texture changes are a lot easier.
For lighting techniques:
I don't have any set "formula" for lighting, because different settings may look better on differently shaped or textured objects. What looks really good on a soccer ball might look really bad on a stingray, and vice-versa. Each object is an experiment.
In general, it helps to have one bright light high up (the "sun" and dimmer lights on the sides, at roughly the same height as the object. This can help make it look like you have more diffused, natural lighting. Experimenting with the side lamps' settings can give a lot of interesting results; you can try making them different colors, or turning specularity off (on the same panel where you change their color/brightness) which will make it so that the object doesn't shine where those lights hit it. That makes it a lot easier to include more light sources, and still keep them subtle.