Well,it's very very hard to explain.. This is the simplest way that i can explain :
-make the cokpit view first,like pilot seat,ironsight,etc
-then make the instruments on another plane designer
-when your instruments is done,save it as sub assembly
-place your instruments on the right place on the cockpit
-TA DA... Your co kpit is done

I know it easier to say than do,but maybe you can see Exumer's tutorial about real cockpit