As with all new techniques, it will take time to get used to using your sewing machine on the frame. Don't be afraid to put some old fabric on the frame and sew, sew, sew. Practice often, don't be afraid of the frame. The worst thing that can happen is a few broken needles so stock up ahead of time, just in case.
Many people make the mistake of running their machine at its top speed or at a very slow speed to start out. Although you may use the entire range of your machine speed after you have a little more experience under your belt, you should begin to practice stitching in the middle speed range on your machine.
To begin stitching, gently squeeze your hand lever so that your machine is running at about half speed (for the rest of this article, we'll assume you're using the hand speed control). If this is the first time you have used your sewing machine on the frame, try slowly squeezing the hand lever all the way to get your machine up to its top speed, then slow it back down to about half speed. This will give you a better idea of the range of your machine.
When you have found a good mid-range speed, try moving your machine around on the frame in small circles, just as if you were trying to get a dry pen to write.
Stop stitching and look at the stitch lengths. If you have large stitches and jagged lines, try moving your machine around in circles again, with the speed of the machine a little bit faster (squeeze harder on the hand lever). If you have tiny stitches and you would like them to be bigger, try slowing the machine speed down a little by releasing the lever, but moving the machine across the fabric with the same speed as before. A good rule of thumb for beginners, is to make your stitches about the same size as hand-quilting stitches, approx 1/16" to 1/8" long. Another tip is to make them big enoughso that they will be easy to remove.
Keep "scribbling" on your quilt until you come up with a machine speed that is making the size of stitches that you like. During this process, you will become accustomed to the sounds your machine makes and be able to recognize the sound of the speed range that you are most comfortable with.
What you have done is chosen a stitch length that is appealing to you. Stick with this stitch length for a while. Try out different types of quilting and try to achieve this stitch length. Try freehand quilting with small tight designs, large loopy designs, following a pattern, or tracing a line that you have drawn onto the quilt.
To adjust your stitch length, there are two things that you can change; your machine speed or your hand speed. At first, try to only change your machine speed or your hand speed, not both at the same time. If your stitches are too small, try speeding up your hands and keeping your machine speed the same; or try slowing down your machine and keeping your hand speed the same. If your stitches are too large, try speeding up your machine speed and keeping your hand speed the same; or try slowing down your hand speed and keeping your machine speed the same.
Sounds confusing, but the point is to only change your hand speed or your machine speed, not both at the same time. This rule is only for beginning practice though. After hours of practice, you will find that you are adjusting your speeds to keep your stitches even without even noticing.
You will find that when you are trying to follow a line, when you are making up designs as you go, or when you are making tight curves and getting in and out of corners, you will tend to move your hands slower so you should slow down your machine speed. If you are doing large loopy designs, or designs that you are familiar with, you will tend to move your hands faster, so you are able to run your machine faster.
Personally, I take a second to think about what I am going to be quilting and think about where I might need to slow down. I start out with a med-slow machine speed and try to move my hands at a speed that gives me the stitch length I like. If I find that I am comfortable and could go a little faster, I speed up my machine and then my hands. An important thing to remember is to try to move your hands at a constant rate, especially when switching from tight difficult designs to loopy large designs.
Good luck and remember to practice, practice, practice!