Running in and out of a line of cones could help for your stepping, and just practice 50-100m sprints (whilst carrying a ball in your hand). Other than that, wing is similar to the other back positions - tackling, passing, and the occasional rucking will be necessary. But these are fairly commonplace, so you will get the hang of it in training or games.
In today's game your winger needs to be more than just the fastest man on the field, you need to work on their attack skills, too. Skills: Catching the high ball. Kicking off both feet. Side on tackling. "Tackle jackle" - the ability to make the tackle and then get to your feet to gather the ball. Staying on your feet until support arrives. Try scoring in the corners. Beating a player one-on-one.
