Principles of modeling?

[nexusbird]

As the title suggests, what are the principles of modeling? I know you have to work with quads as much as possible definitely no five or more sided poly-gons but somtimes three sided triangles are acceptable.

now this is where i seem to think un-logically and struggle to understand some stuff, for instance here are a few things i am unsure about and hope people can clear up for me.

Can geometry intersect?

Does everything have to be connected? for instance can i cut star out of a box and leave it with only one side connected? I see some tutorials where people use splines to make an awesome shape and then extrude it, but the shape inst connected from each side as sometimes its not possible as all you would get is triangles.

Hope to hear some replies here.