Hi Kafla,
I usually put main lead vocals down the centre on top of the bass line. Harmonies slightly left and/or right of centre (depending on effect required), backing vocals a little further still. I try to build textures in to the songs if I can. I always record with the main vocals still playing as it helps with timing and any nuances that might be in your main vocal.
Effects wise I tend to keep the main vocal relatively dry, then apply reverb, etc to backing vocals. Again, it all depends on the type of track and effect you want. If I want to try and thicken my vocals I'll put a very quiet track under the main vocals, or mix the vocals on their own as three tracks, panning hard left, right and centre, then export the master of this back in to my main recording as one track.
I'm rubbish at explaining things, but hopefully you get the idea. Most of the time I find it's trial and error - especially as I don't have a great voice to start with.
All the best,
Digger