Welcome to Gaia! ::

Hello this is my first time I'll be posting art on here.
I just want to hear people's opinions on my art, I am not that good at art and I've only recently started using sai paint so I'm all new to the concept of sai paint.

It looks like these are both sketches of pictures taken from Naruto. Have you started drawing your own ideas out or are you still in the beginning phase of copying other artists? I don't mean this in a negative way, don't get me wrong. I remember doing nothing but copying other's artwork for the first two years that I started drawing anime style. I was just wondering if you have any original work. If you do I would love to see it! ^__^
It looks like you have talent and I like the look of your shading, you seem to know just where to put it. I would just like to see a little creativity and imagination from such talent.

I agree with the two posts above.

As for the images you posted I would just say don't be afraid to take your time with the colouring, zoom in if necessary to colour within the lines or erase any overlap.
Also on the top picture the iris on the left is shaded but the right iris isn't.
On the lower picture I assume the back of the hair should be coloured? Unless it's meant to be split at the back?

Lastly I noticed you saved it as a .png with a transparent background when you do this I'd advise you colour in any areas you want to keep white like the eyes.