For smooth motion you have to make sure the object doesn't move too fast, so that it doesn't move too far between each frame. You add more frames simply by stretching the animation in the 3D software e.g. if currently keyframed at frame 0 and frame 30, to move a certain distance over 1 second, just drag the keyframe at frame 30 to frame 60 or 90 etc. - this will mean the object now takes longer to make that move. You can retime in the video editor (but retiming always carries a risk of ending up looking jumpy again).
Of course also, be sure to enable motion blur when rendering, that might even solve the jumpiness without having to adjust keyframes :)
I don't know if there is any tweening software out there that can generate extra frames, if not, re-rendering with motion blur and/or different frame rate may be the only way.