The trick to sewing pocket linings is to line up the base of both pockets to each other (if you have two pockets), and to use a simple whipstitch.

You will need: a blunt yarn needle and spare dpn's or circular needle.

Start with the sides of the pocket lining. On the wrong side of the body, thread your spare dpn vertically through the back of every second stitch, creating a guide for the sides of the pocket lining.

Here's how to knit seams.

This is important to get right, because picked up stitches are usually at very visible parts of you knitting, like the button band and neck.

Another sometimes-mysterious finishing technique. All those little tails of yarn, what to do with them?

If you google blocking, you'll find a lot of advice and debates. Here you'll find some very useful links.