It's very difficult to give good, straightforward advice on how to develop one's style.
So, I am giving some sideways advice.
First off, your style is going to be built up of words. Therefore, getting to know words is your basic tool box. Vocabulary building exercises may help, but you understand a word best if you meet in its native habitat, in the wild. Read widely. Get to know many words. You can't use "amble" or "trudge" instead of "walk" unless you know "amble" and "trudge." Good words can lead to the possibility of boiling down long phrases into a single word.
Of course, it does lead to the possibility of overloading your prose with sesquipedalian verbiage, rendering it ornate and unintelligible -- but writing is full of risks. Practice helps avoid the
However, reading alone may leave the words in your reading vocabulary. They will do your style no good unless you use them. Therefore, you have to question the words you use, considering whether "give up" or "yield" or "surrender" is the appropriate term.
And in aid of that -- well --
Here is your whip. Practice cracking it a bit. And here is your chair, to fend it off. Now, let's go into the cage. . .
Now, this is the wild thesarus. It hates you and wants you to look like an idiot. Give it the slightest chance, and it will pounce on your manuscript and pepper it with subtly wrong -- and sometime, not so subtly wrong -- words.
Never use it to replace a word with another that you are not familiar with. But as a tool to remind you of the possibilities, it can be invaluable.
(More advice to follow: here and here.)