Critters is a really great resource for original fiction. I think that it's the dominant sci-fi/fantasy web based critique group. (And is for good reason - not only are there a few hundred members, but some are really good - i.e. have won Hugos and Nebulas.) Of course, they can be rather harsh. (I've only had like...one beta who's been as tough as they are.) But, you know, editors can be, too.

Plot is really critical for original fiction. (And really doesn't seem to be for fanfiction, for whatever reason.) So it's good to work on that. Without a strong plot and hook, it's really, really hard to sell anything. (Character driven work rarely does well commercially...*sigh*) But, you know, plotting is a skill like anything else! You can develop it!