One of the hardest things for most new engineers to get a handle on is using reverb in ways that accent the music without distracting from it, or overwhelming it. Part of what makes this hard is that most reverb units and plug-ins aren't terribly useful in their stock incarnation. While you can insert a reverb on a vocal track, for instance, unless it's a rather advanced unit, it won't have some of the things that make it work with the vocal instead of just wrecking it.
So, here's a quick list of ways to use reverb that will at least open your ears to the many sounds you can get quickly that will add polish and vibe without being obvious.
Send it out. First, you should almost always put the reverb on a send, or aux channel. If you don't know how to do that, look it up. This does two things, it reduces the strain on your computer's processor, and it allows you to blend multiple instruments into one reverb 'space,' which can makes them sound more coherent. In the analogue world, sends are usually used simply because many studios have only a few reverb units available.
Pre-delay. You will usually want to have some pre-delay on your reverb. This can be done using a delay plug-in, though some reverb plugs have the function built in. Set the delay to be in time with the music, maybe an 1/8th note, to start with. You can calculate the delay once you know the tempo. 60/BPM gives you the length of a 1/4 note in seconds. So, at 120 BPM, a quarter note is .500 seconds, or 500 milliseconds. An 1/8th note is then 250 milliseconds, a 1/16th note is 125 milliseconds, etc.
Using a pre-delay just gives the source instrument a little room to breath before getting bathed in reverb.
Narrow The Band. I like to use both a high-pass and low-pass filter to narrow the bandwidth of the reverb. Cutting the lows reduces the mud that you'll get, while cutting some of the highs can reduce sibillance, and help to make the reverb less obvious. Experiment with the frequencies. I usually start by cutting below about 400 hz, and cutting above 4khz.
Modulate. Inserting a modulation effect after the reverb plug will give some more space to the verb, this can be nice when you want something big and lush. You can also insert it before the reverb, if the effect is too dramatic. I use a mod delay set to a very slow rate, but you could also try a chorus, phaser, flanger, etc. Try it, you might like it.
Distort the reverb. If you have an amp simulation plug in, combining it with a reverb plug can give very cool results. Using the amp sim before the reverb gives a sound similar to reamping the source in a live room, something that was very common in the days before digital reverb. Inserting the amp sim plug after the reverb plug will give a sound more like the reverb in a guitar amp. This can sound a lot more natural than adding a clean reverb to a guitar with a little grunge.
Gate It. My last trick for today is an oldie but a goodie. Of course, you've likely heard of gating a reverb, to get that 80's snare sound. What I'm talking about, though, is the opposite. Put a gate BEFORE the reverb plug. This way, only loud sounds will have reverb added. This can work on a vocal to accent the sections where the singer is really belting, or you can use it on a snare drum, to add some long verb to hard hits while leaving ghost notes dry. I use this trick once in a while on drums, and it can be very cool.
That's it for today, get out those reverb plugs and start messing around. It helps to think about what you're trying to do before you start, so spend some time with that, too. And automating your send levels can add a whole new dimension to songs, as well.