do you Suggests wash yarn before knitting ??
No, not normally. It's not easy to do and there's no point in most cases. Why are you asking? Is your yarn smelly or something?
NO it is not ...I thought this might make yarn looks better
I've come across instructions for washing acylics that are rough before using them but I've never done it. I generally see no reason for prewashing yarns but there could be good reasons for it.
Sometimes there are yarns with lots of lanolin in them and you may not like working with the smell on the yarn and your hands. I've also had yarn that needed a wash to set the color before knitting but that's another story.