Ok....my 1st colourization. It isn't very good, because well, it'smy 1st one. So if you gave me some tips on how to make it better, that'd be great.
It's thumbed

I just was really playing around w/ it not tryngto make it look wonderful. So, tips on how to make it better, please!
edit//
Here's the before picture:

It's not bad for your first but as some tips I would say zoom in when you do it so that you don't miss spots you missed alot but hey we all do on our firsts. Also try more natural colors like instead of bright green eyes + purple lips try like dim green eyes + lighter lips. More natural colors would work better. But its pretty good for your first.

^Come to think of it I see what you mean. I was going for the light pinkish look on the lipsbut now I see htat they're clearly purple. Lol.

The eyes.... You're only colioring the iris, not the entire eye. The skin color is... GREEN! o.0 She looks sick. And... Models don't let lipstick on their teeth. Ever.
You also didn't color the inside skin of her eyelids. I'd also suggest you use larger images, upwards of 600px. It makes them so much easier to colorize and then you can always resize later, when you're finished coloring it. It also makes it harder to notice the little mistakes.

^ ditto
but its ok for your first try

not bad for your first time. like a lot of people, the colors are just a bit off. one thing you can do to get a natural color, go to image -> adjustments -> curves. mess around with the line on the graph to tone down the color. if it's too green or too red, go to image ->adjustments -> color balance. colourizations is a lot about the eye and finding a happy median.

great job!