The question is too vague. You need to ask a more precise question.
If there are no flat surfaces, you pretty much have to decide what "side" you will machine first. then 2d rotate and line it up from there. It really matters how it will fit in the material you decided to work from.
There are allot of factors in deciding which way to orient a piece relative to machining it. Usually you decide what would be best about when your half way through machining it!
