Once you learn the technique and you understand how to attach the extension, it's really just a matter of trial and error. My sister and I learned by experimenting on each others heads. Basically, we found the easiest way to attach the extension was to do this:
-take the amount of synthetic hair you are going to use for one braid and split it in 2, with one half a bit bigger
-take the 2 strands of synth. hair and loop them. (A braid has 3 strands, so I like to section the synthetic hair in to 3 strands first, that's what I'm trying to descibe here)
The smaller piece will make one strand and the bigger piece will make the other 2 strands.
-so now you've got your ext. hair in three strands. You've got the section for the braid parted on your head, right? So you section the piece of real hair in to 3, you place the extension (which is in 3 strands) over it, and you start braiding under.
The trickiest part about it is the tension, which will only come with practice. Try doing a few on your sister's head and you'll see, it will come to you. When my sister does my hair, I section the hair into 3 strands while she's braiding to speed up the process.
I find that my braids slip out less and and hold better when I start with 3 strands, I know there are other ways of doing it, but that's what has worked best for me, plus I find it easier to braid.
If you already know how to braid somewhat, as long as your parts are neat, it should come out fine. I wouldn't suggest trying to do micros your first time, cause you will probably be slower at first and might have to do a braid over now and then. But you'll get the hang of it. I hope this makes sense, if you have any other questions feel free to pm me.