Today, take a finished piece of your own writing, preferably one you haven’t looked at in at least a month; pull out a short piece of it, no more than three pages long, preferably something discrete (if you have a chapter or other section that short, great; otherwise, break it arbitrarily somewhere). Take a blank sheet of paper and a pen, and, with as dispassionate an eye as possible, go through that piece of writing and note any elements of style you find. Do not use judgmental terms; this isn’t an analysis of quality (for instance, you might write “uses many adjectives and adverbs”, but don’t get tempted to write “uses too many adjectives and adverbs”).
You’re looking for anything that stands out as being an element of your personal writing style, those things you tend to do unconsciously that leave your verbal “fingerprint” on a piece. Are there any phrases you use repeatedly? Do you use many qualifying words (might, perhaps, a little, I think)? Do you use passive or active voice? Do you use predominantly one or two senses, or all of them? Do you tend to describe characters’ voices more than other aspects of them?
Anything that you think distinguishes your writing should appear in your list.
When you’re done, go back through that list and, on a separate piece of paper, write your impressions of those distinguishing features. Which ones do you like? Which ones do you not like? Which ones do you want to explore further, diminish, or change in some way? How can you go about exploring your own, unique voice while improving the quality of your writing? As you write later things, keep this self-analysis nearby. Now and then, do it again with a new, more recent piece of writing and compare the new list to the old one.