|I'd say it would be better to just do it with skates on, unless you would feel more comfortable doing it with shoes on. Everyone has their own learning curve, so no one answer is right.
Also, just for a second opinion, I almost never slide exclusively on my knee pads. I tend to always drop to all fours (knee and elbow pads). You might want to try both ways to see what works best for you. Also, try sliding out fakie and forward. Run up a ramp and 180 to slide down forward. Run up the ramp and and just lay down to slide out fakie.
Good luck training!
: No trampoline here. But should I practice sliding on knees in bowl w/ shoes only first?