Once the skateboard has spun around completely one time, put your back foot on it to catch it. This means that you'll need to be watching your skateboard, to see when it has made one complete flip. This can be tricky - keep practicing. Some day when you are awesome, you'll have a stronger board sense and be able to kickflip without watching the board, but even pros look down when they do tricks, so keep an eye on that board.
Once you catch the skateboard with your back foot, you'll want to put your front foot on the skateboard too.