The best way to slow down your video, Twixtor from Re:Vision Effects
While Premiere has the ability to slow down your footage, and it has a newer higher quality version called Optical Flow (called Pixel Motion in After Effects). It is certainly better than plain frame blending, but it is not the highest quality slow motion you can get. For the highest quality post slow motion the answer has always been the expensive but worth it TWIXTOR from Re:Vision Effects.
Clip speed in Premiere Pro is in the Clip Menu.
This brings up the Speed Panel, and for best results select Optical Flow from the drop down menu.
Twixtor comes in 2 versions, Standard and Pro and is available for a variety of platforms. The version I use is the After Effects/Premiere Pro version. The standard version is $329.95 and the Pro version is $595.00, both fairly expensive, but as I have said quite worth it.
The Pro version gives you the ability to really tweak what the auto track does, lets you use matte’s and alphas to enhance your tracks, as well as splines, and the ability to work with motion vectors from a 3D system. If you have a really important shot to slow down the Pro version is certainly worth the extra money, though you may get away with the normal version. And they have video based tutorials for their effects on their sites, and they are really worth going into to learn the ins and outs.
Twixtor shows up in your Video Effects RE:Vision Plugs-Ins (RSMB is ReelSmart Motion Blur which I plan on talking about in a later post).
The first thing to realize when working with twixtor is it works based on the whole clip as it can see it, so to specify the in points you need to Nest (in Premiere or Pre-Compose in After Effects) and in the sequence the sequence needs to be longer to work on the extent of the clip, so you might want to double or triple your clip in that nest/pre-comp.