No, there are really no such rules. This is where having an eye for these things comes in, either through a natural ability or through practice (or both). It is subjective, but not arbitrary, and it's art but not a black art.
Eventually, you'll develop a personal style for what feels right to you. Many photographers develop a very distinctive personal look. You mention "pros", and it's worth taking a second to think about that, because there, it's the taste of your clients that's most important. If you're shooting small-town portraits, a straightforward look with a little extra "pop" is probably where you want to go. A few years ago, my grandparents had their portrait taken, and while the photographer insisted the soft-focus look was an artistic choice, my grandparents were upset — it wasn't to their taste at all. But if you're a wedding photographer, a "dreamy" look probably won't do you wrong. Or, if you're instead aiming for mass-market "art" sales, judging from what I saw in a gallery in Vegas, you probably want to crank up saturation until your eyes bleed and tone-map until the halos strangle the whole scene. If you're looking for gallery representation, it will help to know the current trends in fine art (even if, hopefully, your own work pushes that envelope). But if you're going for a more lasting sort of art, or are working for your own personal satisfaction, you'll have to be your own audience.
I think "rules" are common for composition because the camera can't do it automatically for you. The camera can balance exposure acceptably, but it can't choose where to center your subject. Those composition rules are usually dubious, but they provide a basic framework and comfortable starting points when you don't know on your own what you want.
If you don't know what look you're going for in visual style, though, you can just pick a preset, either "picture styles" in your camera or prepackaged settings in your RAW converter. In the earlier days of black and white film photography, that wasn't the case, and you can find a lot of collected wisdom (and, as always, more dubious prescriptive claims) from that era. As less-flexible color film came into use, that approach took a serious wound, and while digital brings back the flexibility, it also brings in easily-packaged pre-done "looks", so it's unlikely that patient will make a full recovery.
That said, I can think of one guideline while working towards that style: everything in moderation. This is often expressed as something like: After you get a special effect you like, dial it back to half that strength and go with that. But, like those rules of composition, this is a conservative line, and conservative is rarely a celebrated value in art. So, you might try the opposite: Be bold. Sure, in a few years you may look back at your work with some embarrassment, but at least you won't be accused of being timid.
It helps to be deliberate. Here, infinite flexibility is your enemy. It lets you do whatever you want, and that can make it hard to settle into your own personal groove. So, here's one approach to try.... Put down the digital camera and pick up an old film body. Pentax K1000, Nikon F, maybe a Canonet rangefinder. Pick up several rolls of Kodak Portra 400, Fujicolor 160NS, and Ilford Delta 1600. Or, at least put down the RAW converter and choose a few of those picture styles — a lot of R&D goes into them, so they're actually pretty good. If your camera lets you (hopefully it does) tweak them to your personal preferences (increase the contrast, say), but once you've made some tweaks, leave it that way for a while. You may even want to pull out the, um, "art filters", if your camera does that. Effectively, these settings are the rules of thumb you're looking for, made programmatic.
Spending a week shooting intentionally with the rule of thirds won't make you automatically a better photographer, but it's still a good exercise, because if you do that and carefully review the results (evaluating not just the application of the rule but the overall effect), you'll know better what you want to do instead, and why. Likewise, shoot a few roll of film of different types, or pick a set of presets and stick with it for a while. (If this is too painful, you can always go with RAW+JPEG so you have an "out" if you get a once-in-a-lifetime shot that really, really shouldn't have had that green cast applied.) Having done that exercise, you probably won't want to continue working that way forever, but I think it will help you figure out how you do want your images to look.