When attempting to achieve an even finish, it's important that you are working with an even cake base to begin with. Ensure that your layers of sponge are level, without too much filling in between them, as this can cause the sponge to slide.
Crumb coat the outside of the cake, if needed, and then put it in the fridge until it's chilled.
You can then place the cake on the turntable and lay your icing over. Spread the coating around the top, and then work around the sides until you have your cake completely covered. To finish off with even results, simply use your scraper and make sure it is smoothed over.