Ok, so this is how I usually record myself (hip hop): I just record the whole song and just have key doubles on certain words. I send my stuff off to a mixer who does all that stuff for me. But I always heard people talking about doubling the whole track. Does that mean recording the whole song twice? and then laying them on top of each other? I just want a thicker sound.
There's not really any rules, if you want it doubled all the way through go for it. Yes, it would be trying to do as similar a take to the lead as possible all the way through (if that's what you were going for) in most cases. You can do things like have spots you want to sort of pop out or whatever where you have your lead up the middle and two doubles each panned hard to opposite sides. You can get fairly creative with it, especially if the person mixing is good at getting them really tight and knows how to work them.