Great start to the proceedings mate, Like Dedman says, if you put the effort in to the pre-colour sanding then you will get a better result on the final colour finish.
Check and change your paper often, use good quality sand paper, not Bunnings stuff and you will be right. if you run from 80-100 grit through 120-180, 240-320-400 and then 600 before primer your finish will be great.