They're tricky little devils to catch, aren't they?
Biggest problem I had was getting enough light to keep the shutter speed high as I didn't want to use flash as ours was a bit skittish.
My first set, taken with the 18-55 kit lens consisted of a set of black blurs as the max aperture wasn't enough to get the shutter speed high enough.
To fix that, I got myself a nifty fifty, thinking f/1.8 was all I was going to need. The second set of photos were then all soft as hell, nothing like as sharp as I'd expected them to be after all I'd read about the lens. Turns out that to get the kitten to fill the frame, the end of the lens had to be about 50cm from the little critter. At f/1.8, this gives a DoF measured in (not many) mm, so after focussing, if either the lens or the cat move (and the cat will move) then the focus point shifts.
The next step was to increase the amount of light so I could stop down enough to solve the DoF issues. This involved lots of getting her to play in front of the patio doors.
Further inprovments were gained from shooting from a bit further back and cropping the image slightly, rather than aiming to fill the frame at the outset.
After all this, I'm finally starting to get some semi decent shots, nothing exceptional, but images that I don't immediately send to the trash.
Lovely looking cats BTW. Make sure you get plenty of pics, they grow soooo quickly.
I'll try and hunt out some shots of ours tonight to illustrate the points above.