I would suggest googling the three act structure and the Hero's journey. They aren't the be all and end all but I've always found them a good place to start when it comes to planning a story.
In general, if you don't know where to go next, throw your character into a pit of lava. This pit of lava may be a new relationship, a drunken one night stand, a stabbing, or quite literally a pit of lava. In other words conflict.
My issue is that I can always blitz out the first 'Act'. I love throwing my characters into trouble. Solving the trouble? Not so much. The second Act hits and suddenly I'm floundering. So I use Act I to get to know my characters. When I start to drown I down keyboard, pick up pen and plan my story in a flowchart. What I want to happen. Where I want to go. Usually new ideas will leap out at me. I have a much higher ratio of finishing a story if I've gone through this step with it. The plan isn't fixed. I can add or change or take away as I wish. The point is I have something to aim for.
My best dialogue always comes to me when I'm far from computer or paper. Always write it down the moment you have a chance because no matter how often you tell yourself you'll remember, you won't. If you want to improve your dialogue evesdropping may not be moral but you'd be amazed what can come out of people's mouths.
Reading also helps. Never stop reading. Even reading crap can help because if you can pinpoint what makes it crap then you won't make those mistakes yourself.
As for describing the setting, show it as your character experiences it. Use all the senses. You don't need every detail. Readers will build a picture in their mind of a log cabin or a five star suite and they won't all be the same. It doesn't matter if your imagination put the chair Jack fell over on the right of the room and mine put it on the left. How many of us have seen films of our favourtite books and said 'That's not how I imagined it'? So rather than telling your reader what the surroundings are like, let them know through action only what is important to your character.