Very common prob man, no worries
The cables that come with this kit are dry as a bone, get a good oil/cable lube and go nuts on ALL of them, including the throttle cable - it's very important that it quickly and easily snaps back to idle speed. It's also a good idea to lube the plastic on plastic contact inside the throttle grip assembly, there are a couple different lubes appropriate for that, but I just use a crayon/candle - wax seems to last longer with plastic/plastic/metal friction.
Also remember to route your cables smoothly without any sharp bends or kinks, generally no sharper a bend than what would make a four inch loop.
Just a touch of heavy grease in the clutch arm's pivot and on it's little engagement ramp will also help quite a bit - but you'll need to take the cover off again to get to them.
Usually that's all there is to it, but it'll also get a lil easier with time and use