How do I add variety?

So I'm currently working on three songs- one for my friend, two for my own. The problem is that I'm  not quite sure WHAT one does to really make each and every song release be separate, unique SONG?
Really, my purpose is to make 'different sounds' within my OWN sound. How is this done? 

Hey, lawp. Could you expand a little? I guess i do get that... but are there any advance techniques for making use of those?

listen to artists you like and try and hear what they're doing

try & copy (within reason!) some stuff you like, it's an ear-opening experience :-)

I seem to have exactly the opposite problem...none of my material really sounds much like any of my other material 
 
I think I hear you...most musicians/bands have a certain DNA in their material even though it all varies and sounds a little different...stray too far from that and you loose your audience.You don't want to loose that! If you loose that you will be more like me lol....It's usually the similar aspects of the music that keep listeners coming back for more if they like that particular niche or genre...whatever you want to call it.
 
You are most likely always going to sound like you. The recipe of your music will use a lot of the same ingredients. If you play to your strong points...say you have good vocal and drums..people will hear and associate with that. Your signature so to speak.
 
There are just too many different ways to add variation to discuss it all here...just a few were mentioned but there are sub ideas within those ideas.This is where creativity comes in...I can't really tell you what to add or take away unless I am adding something creatively to your song.
 
I think it all starts with an interesting tune, then interesting lyrics...not necessarily complicated, but interesting. Hum something to yourself...if you like what you came up with decide on a tempo and play or sing it into Sonar to a click...experiment with drums. You'll get better at the process as you go. After awhile you'll start to think to yourself,"that needs bass here", or" I want to add a solo there" etc..You need a direction and an idea where you want it to go. Look at common song structures like VVCBVCC or VCVCVC Make a concious decision on structure early in the game.
 
Tempo,key, dynamics,sound changes,song structure can all be changed and you still sound like you. 
 
I don't necessarily recommend copying someone else. I think there is already too much of that. I would try to be original.