Depends on the surface....
Wet grass expect to slide for miles, Mud/sand stops you in your tracks.
I try to keep the weight off my knees when sliding, Tuck my feet under my butt and lean right back on the outside of my shoes.
That way i can control the slide easier, Lean back to go faster, forward to stop.
Its a case of trying it, do it in the garden, park wherever. Get a comfartable position that doesnt hurt too much and watch to avoid too much impact on your knee caps.
Best bit of advice....
Get knee pads,
No matter how well u play, if u cripple yourself sliding in then u are going no where soon