Answer: Top Spin.
Change the amount of top spin up and down for different surfaces - high (50+) for clay, low (<20) for grass, around 35 for hard courts. Look at your opponents top spin before the match - if you and he have similar skills, but your spin is more suited to the surface, then you are likely to win. If you are at a disadvantage, then use the experience points to add a % to your skills - may be enough to get a big win.
To get your ranking higher, perhaps concentrate on 'lesser' tournaments, rather than trying to compete with Federer, Nadal etc in the slams and IMS