When I play Kasumi I usually take advantage of how her combos can be changed so easily. Variation with her combos is the key to victory especially when mixing up ones with high,mid, low strikes changing levels quickly. A good tactic to use is use the Downforward Downforward+P move when your far away to get her to face backwards. Many opponents think that when your back is turned you will suffer from long animation delays when using a move to snap out of it and the opponent will usually try to go for a strike. Use this to your advantage and hit Down+P to quickly when they get close and do a jumping spiral like attack and follow up with the PP Upback+K combo to knock them to the ground. As they try to do a recovery roll dash towards them and hit Down+F+K and you'll always hit them even if they try a get up attack since this move hits mid level and will counter a low get up sweep due to it's fast animation.