People hate to block. I'm not really sure why, but it is true. I used to as well. Then, I discovered the difference that blocking can make in your knitting, and in the pleasure of enjoying the garment. Blocking helps your stitches blossom to their full effect AND it usually softens the yarn.
Blocking: The act of wetting your garment and shaping it to dry in the shape and dimensions you desire.
Here are the most common questions I get about blocking (and the answers):
Q: Why do I need to block.
A: Blocking allows your stitches to blossom. They come alive. Blocking also evens out your knitting. Do you have a row that looks a little different where you folded it in your bag--blocking will fix that. The most important reason to block is that you can block your garment to the finished dimension you desire (within so many inches up and down).
Q: Do I have to block every time I wash it?
A: If you want it to fit and have the correct shape, yes. Is this somewhat of a pain, yes. Will it smell like wet wool, yes if it is wool. However, if you purchase a nice piece of furniture, you dust it and take care of it, right? Isn't your hard work worth attention? Giving a non-machine washable garment as a gift, include an index card with care instructions. (Not a bad idea to do this even for the machine-washable items since a lot of those cannot be put into the dryer or shouldn't be washed with towels/etc. As a matter of fact, the reason a lot of machine washable yarns say to lay flat to dry is to prevent stretching and so that you can BLOCK!)
Q: What detergent should I use?
A: I've heard all kinds of suggestions. I could only offer my own opinion and that would be Eucalan, which you can typically find at your local yarn shops.
Q: How do you block?
A: Let me use a sweater made of wool as an example. First, I fill my sink with water (not hot water unless you want to felt it). I add in the instructed amount of Eucalan (see label on the bottle). Place the garment in the sink and let it sit for 10-20 minutes to really soak in the water. Drain the water (notice with Eucalan that you do NOT rinse it out). Roll the sweater in a towel to soak up a large portion of the water. Lay out the sweater on your blocking area. I have a blocking board that has a measurement grid printed on it. I highly recommend it, but it isn't necessary. You can lay out some towels and put your garment on the towels to dry. Pin out the garment to the measurements you want. (If using the no blocking board method, measure the size out with a tape measure.) Do pin the item so that it holds the shape while drying. I use T pins (shown below). I typically put a fan on the garment to help it dry faster. I usually let it dry on the top side and then flip it over to dry the other side.
This process is called Wet Blocking. You can also Steam Block, which involves putting a towel on each side of the garment and using a steamer to wet the garment. Then put it on the blocking area to dry, just like the Wet Blocking. When you Steam Block, don't agitate the garment by ironing back and forth--you could end up felting it.
One final note: Do unto the swatch as you will your finished garment. What does this mean? Knit your swatch before knitting your garment. Measure it for gauge THEN block your swatch and measure the gauge. I've found that most knitters will show a difference. If you want your sweater to fit, you need to adjust your needle size to the required gauge on your swatch AFTER you have blocked it.