Learn from the mistakes of others

My problem with dialogue is that I get too involved in the conversation and end up writing a screenplay rather than a story. [I say screenplay because when I write plays I tend to write something rather different. Too much Tom Stoppard, The Bard, and Nigel Triffith in my formative years.]

So rather than writing dialogue try writing without it. Use cut scenes and the like to end wandering exposition. Remember to avoid the teacher's disease and therefore don't attempt to explain everything. Just because you have a fully-functioning world in your head and notes doesn't mean that you have to show every detail in the story. Leave that for the inevitable RPG supplement. <grin>

Try more short forms than a novel. The market is smaller but they are good practice because they are simpler (as they generally revolve around a single idea), and harder (in that it is easy to write verbosely but much harder to write concisely).

You have a good turn of phrase. This helps.