When opening as black and/or white - What principles do you stick by? And Why ?

Move the knights.

http://www.exeterchessclub.org.uk/Openings/10openrules.html

I try to get all my pieces out in the center.  That way I have plenty of options when the midgame starts.

As I said, get the knights in the centre, castle on king's side early, and don't move queen too early.  It works for me (more often than not). 

Then again, look at my rating!!!

and don't forget to castle

Don't trade pieces unless you can destroy the oppoents pawn structure or stopping the king from castling whilt doing so. Also, avoid doubling the pawns. Also, don't go for the quick 4-move mate. Never works; so i guess a good one would be to not underestimate your opponent no matter what rating he/she is.

atack the centre, and make ur knights work together ;o)

                        2nd111xx []'-'[]

Develop my Bishops, and aventaully my Knight's.

To play the opening accurately (Based on theory) and enter the middle game with an advantage or a position I am familiar with.

 As black I play more of a counter attack style using sharp lines of the French or Dutch. 

 As white it is more positional or longer term with Nf3 systems.

I play very solid and unambitious openings as Black and play either drawish and maneuvering or wild and attacking games as White.