The next time you finish tracking a song, and are getting ready to do the mixdown, go ahead and set up several reverbs and delays in your mixer ahead of time. Go for a long hall, a medium plate, and a short room — just get the plug-ins or boxes plugged in and a generic preset called up and ready to go. Do the same thing with a couple of delays — pre-set-up a long delay and a short, slap delay.
This way, as you’re mixing, you can just route tracks through these effects and apply them to taste. You don’t have to disrupt the creative flow of mixing to load up plug-ins or make other decisions.