the videos here are always awesome, but i also found the video at philosopher’s wool amazingly helpful. http://www.philosopherswool.com/Pages/Twohandedvideo.htm it used to only work in IE, but it’s working for me in firefox now too.
i just re-read your question and realized that the video i linked you to might not address those things… i’m not sure i understand the first part of your question, though, the keeping yarn in the back when you’re on the back side… does the fair isle not occur on the back? if so, you’d have to be purling, which means the yarn is in the back when you’re working and it should stay there…
as for using a color you haven’t used, you have a couple of options. you can “carry” it up the rows along the edges , so that way it is available at the beginning of the row you need it on or you can keep it active throughout by stranding it, which is shown in the videos.
The stranding is always done on the WS so when you’re working the RS it’s on the WS (the side facing away from you). When you turn the work, the stranding is still on the WS but now facing you. You continue to strand (and twisting the yarns at color chgs) just as you were before but on the side you’re now looking at.
And, am I supposed to use certain type of stitch per row when fair isle knitting?
As you saw in the vids, etc stockinette is used for FI. (K on RS, P on WS.)