Never give-up, but do make sure rules and boundaries are in place. Too many parents today confuse "giving up" with "not letting your kid run all over you".
Also, it seems like a lot of parents today just wallow in the muck with their kids -- my ex-wife does that. If my 14 year old asks for something I can't or don't want to do, I simply say "no" and move on with the program. My ex will start fighting, which immediately lowers her to the child's level. Always remember that you're the parent, and if you give that up to fight with them as peers, expect a fight any and every time they don't get what they want.
Not to say children are dogs -- i'm saying nothing of the sort... but watch a few episodes of "The Dog Whisperer". Remember you're the pack leader and the members of your pack will be happier and less stressed when they know you are there leading.