How to create super smooth slow motion clips in After Effects that will be edited in Premiere Pro
As 50ndr33 says, you need to shoot/capture at as high an FPS as possible. The more FPS the better the slow motion effect afterwards.

Kronos is also a great plugin, but as he also states - it has some problems when footage isn't linear. If that's the case, you should have look at Twixtor. It's a bit more advanced (and more expensive) but it's better at handling advanced remaps, and gives you pin-point control.