Ooh thats so good for a first try, after only watching a few streams! I think you'll really like painttool sai, i know i sure do, its really easy to use
i have a few tips for you! ^_^
Try not to use an 'airbrush' sort of brush to shade, one with a super soft blurry edge, it gives a sort of murky-ish feel to the colouring! using a harder brush, like the pencil/pen/paintbrush gives a harder edge, but then allows you to blend colours nicely and give a more defined shadow
You seem to have a pretty good idea of colours, but shadowing could be worked on, here's a good youtube series to watch if you're interested (its long but its worth it, and the guy who made it is really good, his videos on proportion will help as well!)
https://www.youtube.com/watch?v=0q-LZVFZuGE&list=PLV2X3tgajVlHkH3FHxm3rLZWqScFTRhtv
He has others on picking the right colours and colour theory, super interesting and really handy stuff to know!
As for anatomy, the eyes could be shorter and a bit more oval shaped, they are a bit too square on the top
look up some tutorials on face placement, i'd recommend getting used to realistic human anatomy, then moving into the cutesy, cartoony/anime look as its a easier to teach yourself the rules then break them, but you can work on which ever you like!
lastly, PRACTICE! don't let this be your first and last drawing, draw as much as you can and you'll get a better feel for the program you use, colours, lighting, shading, anatomy, all that good stuff ^_^
I hope this wasnt info overload or too rude or anything for your first drawing, but i hope this helps! feel free to ask for more help or come to me for any other critiques
You're off it a really really good start, seriously, you should have seen my first digital art hahaha!
