If you were going to add reverb to a song would you add a certain reverb setting combination of wet/dry etc for the vocals and a different for the drums? or would you send all vocal tracks and what ever other tracks you wanted to add reverb to a bus with the same reverb settings?

I have a the reverb on a bus set to 100% wet. Then use the sends from each channel to send how much signal gets to the reverb bus, so the send knob defines the wet dry for that channel.
 
Additional to this I have 2 or three reverb buses, with a different reverb on each; very small room (some people call 'the office', a medium reverb (could be a plate) and hall. So each channel has 3 sends. Each send directed to it's own reverb bus. Then add a touch of each reverb to channel.

ok, cool. thanks. so one song might use 2-3 different settings of reverb?
 

Two, three or more reverbs in a song is common.  You might also want to investigate using delay and chorus.  Delay can add a reverb feeling and chorus can add a sense of width to a mix.
 
It is VERY easy for a beginner to use too much reverb.  In the beginning a good rule of thumb is to add reverb until you can hear it then back off until you can't hear it.