What I normally do when mixing 2tracks and vocals is use a limiter on the instrumental and cut down 3db to give the master fader some headroom. This also allows you some room to work with the vocals. From there EQ and compress the vocals and add some reverb/fx. Typically the type of reverb I use and its dimensions depend on the feel of the track but I only send a small amount of reverb to the vocals so that if you turn it off you will miss it but not so much that it is noticeable and gets muddy when playing with other elements. Too much reverb is just going to make the vocals sit further back into the track. Also, if the instrumental sounds like it is messing with the vocals a bit find out what frequency may be the culprit by sweeping the spectrum and just notch those frequencies out a bit, or try giving the vocal a bit more presence by boosting around 5k...whatever sounds pleasing. One tool that actually glues things together for me is the SSL Compressor try adding that on the master fader.
