Is it easier to do it on slopes as to flat surfaces?

I tried it a number of times (on slopes), I got the sliding animayion but I always fall down, could anyone tell me where I did it wrong?

Neither is "easier" as far as timing goes, doing the bone slide is frame perfect either way. However, flat ground is usually easier since it's harder to tell which frame you'll land on a slope, especially in realtime.

Getting the float is pixel perfect, so it's hard without a setup. If you fall off you were too close to the edge, if you don't fall off but don't get the float you were too far.