Borrow another electric screwdriver/drill so you have two - one with the drill bit to pre drill and one with the screwdriver bit to drive the screws home. Buy a drill bit that drills and countersinks for a neat finish. I cleared a corner of my loft - boarded it and just moved everything onto it and then boarded the rest - depending on the loft - should only take about a day. Think about putting a light up there while you are doing it and maybe a socket - it saves you doing it at a later date and havng to lift the boards.