I teach a Finishing class on a regular basis. It's a popular class, as finishing is one of those things that tends to make knitter nervous.
In the class, I talk about blocking. The first thing I try to do is demystify it: to help knitters understand that it's not some arcane process that requires special equipment and training, or a separate room in your house. All you need it some water - give your knitting a bath!
You need to pay attention to the washing instructions for the yarn, of course. A machine-washable yarn can be treated a bit more vigorously than a non-machine washable yarn. I tend not to steam block, or use spray bottles or any of that.
Here's my rationale: if you're making a garment, it's going to get washed at some stage. So block it the way you'll wash it. (And yes, this is how I block my swatches, too.)
If it's machine washable, send it through an appropriate wash. If it's hand wash only, dunk it in the sink, let it soak for a while, roll it in a towel to wring it out, and lay it flat to dry.
Do I pin it as it dries? Depends on what is it. If it's lace, it needs to be stretched and pinned to open up the pattern stitches.
For garments, if it's the right size and shape, I don't worry about pinning.
If you are sewing something up, blocking is a critically important part of that process. Always block your pieces before you sew up. Three reasons: one cosmetic, two practical.
The cosmetic reason: blocking something magically evens everything out and makes it look more finished. Try it with a pair of socks, or two sleeves, or two mittens - wash one and not the other, and compare how they look. I never declare a piece of knitting done until it's had a bath. Even if it's a piece that doesn't need sewing up or stretching.
Practical reason #1: blocking reduces that pesky rolling on the edges stocking stitch. It doesn't remove it entirely - nothing will - but it will make your edges a fair bit flatter. This helps enormously when you're seaming.
Practical reason #2: If the garment is going to change size or shape - to grow or shrink - you need this to happen before you sew up.
Here's the Violent Disagreement bit: someone recently pointed out that Debbie Stoller, in the first Stitch and Bitch book says that she doesn't know anyone who blocks before sewing up, and she doesn't see the point.
I was shocked.
She's so wrong on this it's not funny. If you sew something together and then wash it, and it shrinks, your seams will be all puckery. And if you sew something together, wash it, and it stretches, your seams will not stretch with it. (Especially because we don't always use the knitting yarn for the sewing up.)
Oh Debbie - your book is otherwise so very good.... I am saddened that we have come to this.