When knitting a sweater with sleeves, once you have the length of sleeves required you have to taper in the top for the shoulder. Usually the pattern tells you at some point to knit two together at the very beginning of the row and then knit two together at the very end of the row. I do not particularly like this method as I find the edges can become "sloppy"
Step 1: Forming a Neater Shoulder Edge Altogether
Instead of knitting two together immediately, I like to slip the first stitch, as if to knit, and then knit two together through the back of the loops. When I get to the last three stitches, I knit two together and then knit into the back of the loop of the last stitch. For all purl rows slip first stitch as to KNIT and then continue in purl.
By using this method you are eliminating the saggy baggy ends that can sometime occur. This method would be especially useful for the inexperienced knitter, where the tension is quite often a bit iffy because of inexperience.
Step 2: The End!
This was not a "real" sleeve that was part of any garment known to man! but just something I knitted as an example to show the method. Below are pictures of the finished sample, back and front.
Also when you have to knit two identical pieces, for example the sleeves, it is a good idea to knit them both together on the same needles using two separate balls of yarn. The reason for doing this is you will be sure to make them both the exact same length and your increasing and decreasing will be done in the same places. Also (and very important!) if you make a mistake with the decreasing, it's not so critical, as you have made the mistake at the same place on both sleeves.