Note that you need to be already somewhat familiar with blender. Tutorials are easily found with a Google search.
Texture your models with UV texturing. Your texture images size must be a power of two, e.g. 256x256 or 512x512, in .png or .jpg format (if you use a jpeg texture, give us the original lossless version [e.g. png] along the jpg one so that we have a lossless version).
Blender procedural materials are not supported and most of what you enter in the material buttons window will be ignored. Vertex colors may however be used.
For static objects, most combinations of scale and rotation will export file. However please avoid giving a negative scale to objects (this is bad practice anyway).