3D printing with blender
You are correct about the walls. Using a Solidify object modifier is probably your best bet. A low Thickness: value (0.1 is probably good) helps keep the walls thin but strong. You can monitor the thickness while you adjust the value from Wireframe view.



Additionally, and this is probably the most important thing to know, your mesh must be clean. By clean, I mean it must all be one piece. No separate cubes, cylinders, etc. that you added while modeling, just one solid piece. Think about it this way. If you have added a cube and part of that cube is inside the rest, it might look good from the outside. But the 3D Printer isn't printing the outside, it's printing everything. So that wall, albeit hidden, that is present on the inside of your mesh will be printed.

Bad:



Good:



Lastly, if you have parts of your mesh that can't be printed from the bottom up, or wouldn't stand by itself, consider adding supports. You can always cut these off later.

Leg added because it wouldn't stand by itself: