When I instruct I tell most people when they go through a slalom they always try to go through the middle of each set of cones. Which is the wrong way. You want the rear inside tire running over the front left or right lip so that your car would look something like this:

/ or \
o o

You should still be making 'esses' or 'S' through the slalom.

Another way to do slaloms is to pace the distance between cones. Sometimes the distance gets smaller which means you have to slow down. Sometimes the distance increases which means you can add more throttle through them. And sometimes they are offset so you can either drive a straighter line through them or not.