The first tip is, try to think like a drummer(IOW, don't program something that a real drummer wouldn't or couldn't play). Next thing, if you are trying to lay down a triplet fill, but the grid is set to straight time, the grid will force things to NOT sound right(just the nature of how the grid works).
How are you inputing your midi notes? If you are doing it all with the pencil tool......OMG, how tough that must be! I use an M-Audio Trigger Finger and it works really well as I can tap out like on any good drum machine(good drum machine.....is that an oxymoron
). I also set up a custom pad page with each sound for snare and toms are assigned to dual pads. That way, I can actually tap in complicated rolls and they actually sound good(I use SD2, but the Slate drums should work much the same). Akai makes a similar unit and even the cheap Korg Nano-Pad would likely get the job done.
Also, I try to NOT use input quantize as it can totally remove any feel(real drums don't always hit right on the grid). Sometimes I will quantize things and then go thru and move random notes slightly off the grid, depending on how they mesh with other instruments.