How to build better bumpers and grilles

At a recent contest, I had an unfinished project on display that featured scratchbuilt front and rear bumpers. One of the most-common questions was, "how did you do that?" I went on to explain the process, and one person commented, "Oh, so you just carve away the plastic that doesn't look like a bumper." I agreed, but later started thinking that it is exactly what I do. The process is really not all that hard, and I find it's quite a bit of fun.