Weights before cardio. Do compound exercises (that work more than one muscle group at one), as opposed to isolation exercises. So, look at bench press, lat pull downs, etc rather than, say, bicep curls and what have you. Legs slightly different to that rule, in that the ones you are doing are good. Maybe try squats once you get more confident, but you have to be very careful with the form.
I've had similar knee problems (6'5" and xxstone!) and find cross trainers fine. However, each knee injury is different, so give it a go. I'm utterly diabolical on a bike for some reason, whereas my mate who has had a similar injury story to me rides all over the shop.