The behavior of a 4wd vehicle is so varied depending on the type of vehicle, and the type of 4wd system used that there is no single set of guidelines that would be really ideal...
Here's my favorite tip:
4WD feels more IN CONTROL when you are in control, and is dramatically more OUT OF CONTROL when you loose control. False sense of security is common in 4WD vehicles.
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With that in mind, you mentioned you don't have a 4WD, consider the following....
If you are taking a passenger sedan to places where ordinarily only off-road capable vehicles go, be prepared for the possibility of doing damage to your vehicle. Slow speed driving on tough terrain can over-heat engines and automatic transmissions. Or, in the case of a manual transmission, you can expect to spend a lot of time slipping the clutch to run slow enough to prevent massive damage. Most truck/suv style 4WD vehicles are geared properly to operate at low speeds without the need to slip the clutch or work the engine hard (dedicated low range in the transfer-case), as well as provide more than sufficient cooling for this application. Bumps don't often look as large as they actually are, the right dip followed by a small rock in the right place and you dump your engine oil in 2 seconds flat... Clearance is a must for rough conditions. Some sedans fair better than others. Short wheel base light weight sedans/hatchbacks with more than average clearance with slightly over-sized tires can go lots of places if you're careful, choose proper lines, and let it cool off as necessary if needed.
I've seen people beat up their cars pretty bad taking them just a few hundred feet off the main road on what would be considered a very mild 4wd trail. Be careful out there and take it slow... If you hear "BANG" shut the engine off, get out and check for fluid loss...
-Eric