For any knitting project, the final step is always blocking. Blocking knitted garments is a process that can be used for handmade or purchased garments, but as a knitter it is especially important to learn how to block a knitted garment as it is a crucial step in finishing your projects.
Blocking knitted garments is the process of shaping the garment by getting it wet to increase flexibility and then laying your item out and using straight pins to tack it down. The end result will be a final product with better defined edges and a symmetric appearance. We all know that sometimes our blankets end up a little wider at the bottom than at the top. Blocking is how we can correct that.
For some casual garments, perhaps blocking isn't essential, like a one-piece sweater that is meant to be a wear-around-the-house type of item. But most garments will benefit from the shaping that blocking provides. And a multi-piece garment must be blocked before the pieces are sewn together to ensure that you have the best edges available and that your pieces are all the same dimension and will fit together as they should.
As with all blocking, the key is to wet your pieces thoroughly. When I first started knitting, I had the idea that I shouldn't use much water because I didn't want my yarn to get too wet. Then my early pieces weren't shaping as well as I wanted. I soon learned the problem was that I wasn't using enough water. Really douse your pieces. Submerge them entirely. And as you're blocking, don't be afraid to dump a little more water. When I block, I keep the bucket that I've used to wet my pieces by me and a small plastic cup so I can dip back into the water and add more to key spots as needed.
Blocking a one-piece garment has its challenges as you want to keep both front and back even and square. Like trying to iron pant legs, you want to make sure that the underside of the fabric doesn't have a hidden wrinkle. Using a measuring tape or blocking mats that are lined with measurements will help you ensure you aren't making one sleeve longer than the other.
When blocking a pieced garment, you will also want to measure your pieces as you are blocking to make sure the edges you will sew together match up. I like to block my multi-piece garments out next to each other. When I blocked my dad's cardigan, I put the largest piece, the back, in the center of my blocking area. Once I had that piece squared up, I put the two side panels on either side of it, matching up the side seams. Then I blocked the two sleeves next to each other so they would be the same length while carefully measuring to make sure the sleeve caps as blocked would fit the sleeve holes as blocked. Sewing the final garment together will be so much easier if you've blocked it well.
As for where you do your blocking, blocking mats are a great idea, especially the kind that are lined with measurements like a fabric cutting board. But I don't own those, so I use my guest bed covered in a thick layer of towels. The bed gives me plenty of space. And between the mattress and the towels, I can really jam my straight pins in and have them catch.
To learn even more about blocking, particularly when it comes to various methods and how to block a variety of different garments, take a look at Blocking Handknits, taught by Kate Atherley. Atherley guides students through the process of blocking everything from socks to sweaters, as well as address proper ways to care for a knitted garment to ensure its longevity.