One of the differences between sewers and knitters is that sewers tend to do a lot more pre-work to perfect the fit of their garments. A sewing pattern is just a starting point and many of them will sew a "muslin" before cutting into more expensive fabric.
A muslin is a mock up of the intended garment sewn from inexpensive cotton muslin fabric. If you take this idea and apply it to your knitting you will be able to customize the fit of all knitting patterns for your garments to your individual shape or for the intended wearer.
As a knitter instead of using a woven cotton fabric you can substitute a medium weight knit fabric. You want to choose something with a little stretch as your knitting also has stretch. If you have a specific pattern in mind you can use the schematic measurements to draw the pattern out and transfer to the fabric adding seam allowances. An alternative is to buy a sewing pattern meant for knits. Look for something like this http://www.jalie.com/women-s-twin-set.html or look for a pattern close to the silhouette you would like to emulate. Cut out your mock up and sew it up. You can do this by hand or machine if you have one. Sew everything together with large loose stitches as you may want to tear them out and re-seam as you correct the fit. The neckline will be a raw edge so you need to run a row of stitches along the edges to stop it from stretching out when you put the mock up on.
Now look at the length and mark where you usually like your sweaters to hang to. Check the shoulder line, is it in the right spot? If its too low or too high mark the correct spot and then remove one sleeve and move it up or down as required. Once you are happy with the shoulder line mark the hem of the sleeve. Mark more then one length of hem so that you will have a permanent record of various lengths for future projects. Mark where your natural waistline is. Look at the neckline and decide if it's too high or low. If the mock up is too tight cut it open and use safety pins to add fabric where is it required. Use pins to make it smaller if necessary Once you are done you can transfer back to the paper pattern any alterations you made and as well take notes of the measurements that you prefer. You will use these details going forward to compare the pattern measurements on knitting schematics and then change them to more accurately fit and flatter your own body. As an example you can use the length measurement to get the bottom edge at the right spot for you and make sure that any waistline shaping is at your natural waistline by either adding or eliminating rows of knitting as required.
This post is a basic starting point for fitting I will write future posts on specific fitting issues so watch for further updates and if you want me to cover a specific topic let me know.