I think of reverb as being kind of like ketchup, namely the right amount is supremely tasty, a bit too much can over power and ruin the flavor. What constitutes that sweet spot is of course personal taste, but finding the right settings to achieve that goal can be daunting, particularly considering the number of parameters in many reverb plugins.
Perhaps the simplest manner is to start with presets. Find something that kind of suits your tastes, and edit the parameters from there. However, if you want to start from scratch, and forge your own sound, some advice might be useful to get you started.
The two most basic settings for reverb are the mix (or wet / dry balance) and reverb time. If you think of a real reverberant space, reverb time is the amount of time it takes for the sound to dissipate (technically for it to drop 60 decibels in volume). The mix (or wet / dry balance) would be the distance from the original sound source. For instance, having the mix near 0% (or dry be loud with wet turned down) would be close to the original sound source. A mix level nearer to 100% (or dry being quiet, with wet turned up) would be far away from the original sound source.
When I start building reverb from scratch, I like to turn up the mix to 100%, so I am listening only to the sound of the reverb. Once I get the sound where I want it, I can dial the mix back until I like the balance of the dry and reverberated sound.
Once I set the mix to 100%, I next set the reverb time to set the size of the virtual space of the reverb. Do I want a small or a cavernous sound, or somewhere in between. To sound realistic (which is not necessarily important), it is best to stick to times under four seconds.
Then I like to play with any setting that would determine the size of the room. Subsequently I like to modify any setting that changes the tone color of the reverb, such as low frequency levels or high cut levels. If you are looking to emulate a natural reverb sound, you want to cut out some of the high frequency components, as that frequency range tends not to reflect off of surfaces very efficiently. Finally, I like to move on to other settings that control aspects like density and diffusion.
Again, once I am satisfied with the overall sound of the reverb, I mix in enough of the dry tone so the original sound has enough presence, and the reverb fades into the background. During the process, you will probably adapt to the sound a bit, so most people tend to use more reverb than is necessary. For this reason, it is advisable to listen to it again the next day when your ears are fresh and dial it back a bit if so desired.
That being said, reverb can be a great tool for hiding thin or poor tone quality (particularly on vocals). It can also be used to mask small mistakes. Overusing reverb in this manner as a crutch can result in you not addressing more fundamental performance, recording, or editing issues that can be fixed with a little extra experience or practice. However, when you find a reverb sound that you like, save it as a preset (using a name that is meaningful to you, or relates to the specific project so you will be able to recall it). Saving your own presets can allow you to build a catalog of your own sound. But remember that a little reverb can go a long way. Avoid slathering it on too much, unless you want something that sounds very effect-y in nature.