Character Stuttering/Jaggering in 2dGame

How come my character is stuttering/lagging/jaggering when in playmode?

I have created this script, following a YouTube tutorial called "Unity RPG Tutorial - by gamesplusjames"

My problem is, that the player is like lagging or jaggering or what you call it, while moving.. it's not seamless, if you know what I mean..

And also.. Is there any other way to write the script?, because I searched for other tutorials on youtube, and their code is way different than what this guy is teaching.

Please help me, with both the solution to the laggy, stuttering movement, and also, a better tutorial to follow. for a 2d top-down game! link text