fit the BB Cups into the frame, then screw the drive side BB on to the crank arm so it's tight and flush up against the chain wheel/spider, then put the loose baring cage on the crank arm so that when you thread the arm through the barings are on the drive side....then thread the arm through, put the non drive side on and screw tight.......not too tight though as it'll be hard to pedal, then tighten up the locking nut which should hold it all tight.
hope that makes sense??
oh and don't forget lots of greese!