Technique for parting a part

While I'm still very much a newbie, I have a question I just can't
seem to figure out.

If you start with a billet of say aluminum and you want to cut out a
part, what are the stratagies for removing the part from the excess
stock material? Should I program my NC code to cut all the way
through into some scrap material?

Also - how about cutting 2 sides of a part? Would you generate NC
code to cut the first side, then flip the part and run NC code to
cut the other side?

Thanks everyone, you have been most helpful in getting me up and
running in the world of CNC mills and lathes.

Rob