Quote - When I export the character as an obj, or 3ds, its very tiny.

This is normal due to Poser's internal scale.

Quote - How do I increase the size (scale) of the model before I export it?

Use the Scale dial (for a figure make sure to use the one on the Body actor).

Your question suggests that you're importing into another program, so unless you're making morphs, you might be better scaling up in the target application.