1. Start with a Recipe...
I like outlines. They give me a chance to see if the mechanics of a story will work. It's in the outline that I usually see (and try to fix) the biggest issues with plot. Depending on the story I may have a very detailed outline or a very vague outline. But I've never written a story that I didn't have some idea from the get-go where I wanted it to end. Know what you're trying to accomplish before you start.
2. ...But Don't Be Afraid to Improvise
Even when I pre-plan a story, even when I outline in minute detail, I always hit a point where I just start making shit up. Maybe it's adding a scene I hadn't anticipated. Or turning the entire plot in a different direction because my Main Character turned out to be more of a coward than I had anticipated. Even when I think I know where things are headed, there is always room for change. Don't be afraid to put The Plan to one side and go with your gut.
3. No Matter How You Slice Them, The Onions Will Make You Cry
Every author enjoys some part of the writing process and HATES some other part. For some of us it's trying to finish that all important First Draft. For some of us it's looking at that messy First Draft and figuring out how to make it better. For some of us (me) it's the nit-picky line-editing stage. (Typos are the bane of my existence. And commas. And making sure that every word that should be in a sentence actually is.) For some it's the process of selling a story. But no matter which part you dread, if you want a readable, sellable and published story you have to wipe the tears off your cheeks and muscle through.
4. Even If You Don't LOVE Something, You Can Still Make it Well
I'm a big believer in writing what you love. But (BUT!) I do think it's possible to write a story that you are not completely enamored with and still produce a solid piece of fiction. I say this for two reasons. 1) You may - at some future point - be asked to edit or rewrite something in a way that was not how you first envisioned it. Have faith. You are capable of making changes to suit the needs of someone else. Even if it's not how you would do it. (Of course, whether you want the sale badly enough to do this is a whole 'nother discussion.) 2) You will - if not now, then later - have a story or two that you just don't like as well as the others you have written. This doesn't mean they aren't any good or that they aren't sellable. Trust your skills and submit that puppy 'til it's published. (So far, three of my five sales were stories I wasn't "sure" about.)
5. Getting It Right Takes Time
Some things you just can't rush. I'd like to say that as I've improved as a writer, my ability to turn out stories every week/month has gotten smoother, more dependable. Alas, that is not the case. My ability to tell stories has improved. So has my ability to sit down and write when I say it's time to write. (No more hanging around waiting on that damned muse to strike.) But writing is still work. It still takes effort. Finishing a story can still take weeks. (Or months.) That's okay. Some things come together quickly and others require a more elaborate process, but getting it right is worth the effort.