I have wondered this for MANY years and thought I would ask everyone here. When your doing a 16 beat section and you have variations in it, would you make the variations on the last 8 beats or the first 8 beats OR the whole thing? This comes from working on a "lead synth" variation for a dance song. I understand you can do it either way but for it to sound professional, there has to be a set way to do it so it doesn't come across wrong.. I probably didn't explain my self correctly here but it is worth a shot.
 
Thanks!
Boomer
Edit: Say you have a set pattern for a lead synth. In that set pattern you have keys. In those keys, they can be changed up or down a note etc. on certain parts of that pattern. Would it be correct to do those variations on the last 8 beats of that pattern or the first 8 beats part? Most from what I can tell, keep the keys the same all the way through the pattern tho I like to vary the keys so they dont sound so repetitive.

I'd say it doesn't matter

If it sounds good it is good

I agree - if you took a song by Cheap Trick, for example, Bun E Carlos tends to play very similar patterns for verses, but introduces variance at the end of sections.  Similar orchestrations are present in many Beatles tunes.

At the other end, if you listen to a song by Yes, Bill Bruford would deliberately strive to ALWAYS have slight variations in each measure, even if the basic beat itself is constant.  He accomplished this by varying kick/snare timings, as well as high-hat strikes.

It is partly a stylistic thing, but it ultimately depends on YOU developing your own approach to each song you create.  

YOU get to decide what sounds good, and my recommendation is that you write for what sounds good to YOU, as the other poster summed up "If it sounds good, it IS good".

Bob Bone