i think idea and execution are related to one another. it's hard to separate them...they aren't one and the same but i think there's some kind of "co-exisiting" dynamic between the two.

but.

depending on what stage a piece is in, it can make sense to separate them because sometimes, who really knows why, one gives birth to the other. it's possible to have the idea but not have any idea about how to execute it.

i'm only guessing at what you could mean by execution, by the way.

check to see if your idea is sound.
check to see if your execution is sound.

usually, you don't need to see both. usually. if you can manage to just fiddle around with one, the other will eventually swing into place. i think i place more importance on execution-- how an idea is expressed. it doesn't hurt to be open to an idea evolving and changing, too.

and yes, revision is definitely a piece of the puzzle.

one thing that can improve execution? besides reading, imitations. imitate, imitate, imitate. try on the voices of other writers, imitate their syntax and all that good stuff. pick a topic or emotion or something to describe and put it into a "container" in the style of capote or woolf or joyce or baldwin or whoever. grab one of their novels or essays, pick a section of it, say a paragraph that you like and imitate it. flex your muscles a little bit that way. pick writers from all over, even writers you don't necessarily feel excited about.