There are lots of ways to make polymer clay bangles, even the solid, round or mostly-round ones, but I'm guessing you're just going for the basic very-round bangles that are baked on a cylindrical form.
Here are loads of examples of polymer clay bangles though:https://www.google.com/images?q="polymer+clay"+banglehttps://www.google.com/search?q="polymer+clay"+bangle
--blending the join between the two butted ends is almost impossible to do neatly!
It's helpful to cut the ends at a slant rather than straight across, and then lightly press/wiggle and even stroke them lightly together to join the seam. (If any smearing occurs, it can be sanded off later**.) You can do that with 2 ends by overlapping them side-by-side, then cutting through both at the same time (on an angle) with a long sharp blade; then joining.
Even when joining clay rod ends that have been cut straight across, you can press them together a bit then pick up and gently roll the join between your fingers rather than just rolling it on your work surface.
Also letting the clay parts sit together awhile (even overnight) will increase the strength of the bond by letting plasticizers from each end leach into the other end, or you can try putting a tad of liquid clay on one side or Diluent (now called Sculpey Clay Softener) tho best to let absorb a bit, or just rub each side gently to warm and soften a little.
The rest of any shaping is just kind of pressing or rolling around or on the surface, etc, till the join looks good and is the same diameter as the rest of the rod/bangle.
Or you can do what some clayers do which is just to put another bit of clay around the join
so the seam won't show at all. You'll see some instances of that in the links above.
--after wrapping on can, any attempts to texture, decorate, or even join the clay made it stretch bigger, becoming loose on the can
Texturing and embellishing the clay is often done before making it into a circle and baking.
Those things can also be done on the form (cylinder, rod) but if you're using a soft clay (Sculpey III, Craftsmart, or even FimoSoft especially) they'll more easily distort and stretch and especially if warm..those first 2 shouldn't be used for bangles at all though since they're weak after baking in any thin areas and bangles are "thin".
If you want to do those things while the clay is on the form, make sure to use a form that's rigid (not like a toilet paper tube or even empty aluminum soda can--maybe a stiffer metal like a regular food can, or fill your soda can with water--it can be baked with the water), and also perhaps even smooth (like metal, etc) so that the clay will tend to stick to it and not stretch as long as your texturing/etc is applied straight down (and gently).
--with many bracelets on one can, there was the risk of bracelets shimmying down can during baking, and touching each other
If you want to bake more than one bangle at a time, you could use more than one can (preferably a stiff-metal can) or that one can could be cut into segments.
You could also lay the can down while baking (preferably on a nest of polyester fiberfill or pile of baking soda to retain the bottom clay's shape while it bakes--and softens), or you could make some kind of horizontal rod or cording it could hang through while baking.
You could also put something between the bangles on the can, but nothing that would leave an impression when the clay softens during baking --perhaps a strip of polyester batting, or a tissue or piece of cotton fabric folded-over to make a strip, or something else.
So far, they DO seem sturdy (baked a couple times for extra hardness), but i feel that i have little control using this method.
Baking any polymer clay longer will polymerize it more and more and therefore make it stronger (though more likely to darken if not protected***), but it's also important to use brands/lines of polymer clay that will be strong enough after baking when they're used for "thin" items like this. So as mentioned above, Sculpey III is not a good choice even though it will feel "harder" than the strong brands; Kato Polyclay and FimoClassic will be strongest, followed by Premo and Cernit. FimoSoft is not quite as strong.
(Not sure what you mean in this sentence by having "little control using this method.")
You might want to look into the other ways of making bangles with polymer clay, which include all kinds of methods like making the bracelet in two parts with a hole or channel running inside each one, then using elastic or two elastics through them both; making the bracelets over a pre-baked polymer core, or over a non-clay armature of some kind; making the bangle flat on the inside; etc.
Here are a few tutorials for the simple round-solid ones I just ran across:http://www.ericabunker.com/2011/07/diy-clay-bangles.htmlhttp://www.craftster.org/forum/index.php?topic=386183.0;allhttp://www.craftster.org/forum/index.php?topic=403419.msg4746725#msg4746725
more of maxevv's bangles (scroll and click through the pages):http://www.craftster.org/forum/index.php?action=profile;u=185541;sa=showImageshttp://www.flickr.com/photos/49820850@N03/sets/72157623980119666/with/4573176231
And you can get lots of info on making bangles in all kinds of ways as well as other polymer clay bracelets, if you're interested, on this page of my site:http://glassattic.com/polymer/jewelry.htm
...for the type you're doing, click especially on "Cuffs" under the Bracelet category (though unfortunately many of the actual links have been broken by their owners)
(click especially on "Darkening, Scorching")