Focus on one pair at a time. If you spot a green white piece and go looking around for it, dont change your mind during that process (unless you see a really easy case). You just need to get the edge pieces in the 2 middle layers on different levels and slice until they match. Don't focus on getting them next to each other so that a 90 degree slice is enough since it doesnt matter what happens to the 4 centers. You can slice however you want.
Other than that, practise practise practise.