If I reread something and don't like it, I edit it until I like it. If it's that bad, I rewrite it (the scene, not the entire thing at this point, but I have gone back and rewritten entire novels before). Don't worry too much about bits of your first draft being not as good as you want - that's what editing and/or redrafting is for. No-one's going to see your first draft unless you want them to (and why anyone would want anyone to is another question).
I don't do metaphors and similes. Or at least not usually (I might occasionally throw one in here and there). They're nice, but they're not essential. Definitely don't force them in if they're not coming naturally because the result is excessively flowery, purple prose. Focus on telling the story and not boring or confusing the reader. There are lots of good writers that don't do metaphors and similes all that much.
What makes a good story isn't the premise, it's the execution. (So forget worrying whether your premise is good enough.) And the way to improve your ability at anything is to keep practicing. Writing's no different to any other skill. Those things you wrote that you don't like? The fact you wrote them at all means your skills improved from writing it. The next draft will be better (or if you just edit it rather than redrafting the whole thing, the edits will make it better). The next thing you write will be better. The process of rereading it and editing and/or redrafting it will hone your skills. When you're rereading, if you don't like something, don't get discouraged by it, instead analyse it... why isn't it working? How can you make it better?
Have you done any critiquing or put your work up for critique? You can do that here when your post count's above 50 (share your work section). Personally, I've found that reading loads, rereading and editing my own writing, writing loads, critiquing others and getting my work critiqued has been what's led to the most improvement in my writing. While there's always going to be differences in how different people learn, I'd say that the vast majority of writers benefit from all those things.