Not a lot of experience with Lego (only few stop-motion videos) however what you need is:
- A tripod for your camera
- two light sources.
If you don't have light box, use a spot with some diffuser on it (milk bottle, white tissue,...) the goal is to have the light not comming from a single point but from a whide surface.
Place the camera, on the tripod, in front of your model and dispose one light on each side.
Now look into the camera for flare, if there is any, change the position of the light source (remember the light reflected from the surface will it your camera only if its come from the right angle, moving the source will send the reflexion out of the camera)
With some patience you should be able to adjust the light and get the shot your models deserve.
PS. if there is some unwanted shadow you can add another source of light or use a small reflector (a sheet of white paper is perfect)