3D printers have a certain volume that cannot be expanded. If your model is larger than the build volume, either break it down into smaller pieces or cut connecting lines through the model. Model sensibly.
Always leave a gap.
When designing moving parts of a 3D model, always make sure there is a gap between them. This gap must be at least 0.5 mm to avoid sticking and to ensure unhindered movement.
Keep it stable.
In the slang of 3D printing there is a so-called “thin arm syndrome”. You must not leave any thin arms with unsupported weight at the end. Especially after reducing the size of a model you should make sure that the arms are strong enough to hold it. In addition, Shapeways reminds you that your 3D model is always on your feet, while a real one can tip over. So consider the size of a character and the shape of the contact area. It must not be much smaller. Or remember that you can always add an artificial base for the stability of a model.
Model characters accurately.
When modeling a printable 3D character, you need to pay more attention than ever to detail. Even the smallest part plays a role. Make the arms and legs of your model strong enough. Imagine Shrek standing on two tiny legs. Remember that all surface details must be supported on at least one side of the other surface. The thickness should not be less than 0.4 mm. Fingers are vulgar parts of the body and are highly likely to break first. Try to hold them together.