My thoughts on ring flash are well documented in the thread that Jewelltrail referenced.
But I'll address larger issues here. I think you have to decide how seriously you are going to be about learning to shoot macro. To do it right requires a fair amount of discipline (plus luck, but that applies to all photography). This is not snapshooting.
I recommend Bryan Peterson's book
Understanding Close-up Photography. Great illustrations, and very comprehensive. I learned quite a few tricks and new tools. His enthusiasm for shooting anything closeup is contagious.
I suggest you procure the following: a good tripod, preferably one that has horizontal plane shooting functionality; a cheap wireless remote, an external flash with a diffuser, a Pentax hot shoe cable footing--get the taller one that allows the popup flash to open, and a 2-3 foot cable to run from the camera to the off-camera flash.
The tripod is necessary to prevent camera shake and ensure a "crisp" photo. It will also free up your hands so you can manipulate the flash. It will also let you shoot longer exposures which are critical when using apertures such as f11-16. The remote keeps your hands off the camera once framing, focus, and exposure are configured correctly. A tripod also helps ensure consistency which is a requirement for excellent photography.
From your initial post I assume you don't have an external flash. In my book just about all photographers who are going beyond snapshots need one. While the range of available strobes for Pentax DSLR can go beyond US $400, as a starting point as well as for macro use, I'd go with something cheaper.
I'd suggest an old-style thyristor-based flash that allow full manual control. PTTL won't serve you well with closeup shooting anyway. Plus it's critical for a photographer to learn to use a flash manually when shooting in M mode on your camera--which is the way to go for closeups.
Something like a used SunPak Super 383 works great (for me at least). You can lower the power output to 1/16 with a very convenient slider. There are also three levels of Auto flash, so you have plenty of flexibility for all shooting possibilities. It swivels and tilts too. Plus it should run under $65 USD, but you may have to dig a bit. There are other good cheaper strobes too, so check the Strobist site and here.
Stick a diffuser on the flash to soften things, attach your cable, and then have some fun. With your camera set on the tripod you use the flash in so many ways. You can supplement the existing lighting--often quarter-shadows obscure the scene too much. Or you can create drama with intense shadowing. Or you can just dominate the natural lighting and control the scene completely. And that's just outdoors I'm talking about.
Technique: with both ring flash and external flash you will get a lot of light. I often use ISO 100-200, f11-16, and an exposure between 1/45-1/125. You may need to go to 1/180 if the wind is a factor. That all said, I've gotten fine shots up to ISO 800 on my K20D.
Lower ISO is preferred because on screen you can see the noise differences with macro--especially if you are cropping. Macro shots, more than a few other types, draw viewer's eyes closer in, so sharpness and noise management is more critical. A print, most likely, won't reveal those issues, so your output requirements need to be taken into account for ISO selection.
If you are shooting with more wide-open aperture (which is one of my favorite things too), your flash can be held further away for just a touch of light or some fill. Experiment. And have fun.
M