sweet! Like I said I pretty much love Sai all over the place and use it for about everything, I love how it outlines because it makes my lines so crisp and clean! But yeah I use it mostly for sketches, outlines, and flat coloring (sometimes shading). Tho details I usually use Photoshop..but not the point. I found that has a youtube channel that she shows off some of the things that she works on, and Ive found it really helpful in learning how to do things. She does have a small tutorial about line art and coloring but if you watch her speed paints you can see more advance ways. [link]
Course as always you'll find your own ways to go about things and what works for you. But I will say that Ive found that my work time pretty much gets cut in half because of the things that i can do in Sai that I couldnt do before in OpenCanvas and PS. Anyway tho if you have questions about other things feel free to ask!