Godfather said:
does this happen to you. you get an idea, think oh! that'll make a great short story. then you set about writing it, and it comes out so desperately bad that you don't know wether to laugh or cry. so get other people to do it for you in your head, hey presto, a new idea which you **** up again
I think this is a dilemma all beginning writers face. That's why it's so important to write as much as possible.
As time goes on, I've found that the distance between what I think and what I write has decreased. I'm definitely not where I want to be yet, but I'm definitely a lot closer than I was a year ago, a month ago, a week ago.
They say you have to write at least 100,000 words of crap until you finally begin to actually write. I believe it.
Like anything else - the more you do it, the better you get. Just keep writing and don't let yourself get discouraged.
The road may be long and rough, but the more you walk it - the more accustomed your body will get to walking it and the more distance you'll be able to cover.
Then, hopefully, before you know it, you'll have reached your destination - but even if you don't, at least you'll have enjoyed the journey....