In terms of style in D.H. Lawrence's short story, "The Rocking-horse Winner," I would concentrate on the author's ability to convey a sense of urgency in the style with which he writes.
A great deal of the feeling of urgency comes from the mother's treatment of her children, acting as if she loves them, but not able to love anyone. Only she and her children know. This will be important in that Paul seems to correlate success in making money with earning his mother's love. I would include this, perhaps with a quote from the beginning of the story, using quotes of words and phrases that support "urgency" (...from the author's choice of words, descriptions, etc.).
I would also support your assertion of the author's ability to imbue the piece with an impression of urgency using the description of how the house seems to echo the mother's obsessive mantra, "There must be more money." (The repetition of this phrase also shares a feeling of urgency.) The mother's obsession is passed on to her son Paul. I would correlate, as well, Paul's sense of "luck" and its connection in his mind with "love."
I would then make sure to include how Paul learns of his "gift." I would describe the mania that seems to come over the boy as he rides his rocking-horse: a physical description of Paul would be appropriate. I would include how savvy the boy is in getting money to his mother the first time (so she doesn't know where it is coming from—and his excitement): and how she blows it all. (The feeling of urgency may slow down here for a short time, until the mother's obsession begins again.) When given a great gift, regardless from where it comes, Paul's mother has no clue how to spend it or appreciate it. This introduces the idea that no matter what Paul or anyone else might do, she will never be satisfied. It is like trying to fill a black hole in space. Find text that supports this, focusing still on Lawrence's style. (Unfortunately, Paul is too young to understand that he is trying to achieve the impossible, and his sense of self-worth is based on being able to make his mother happy.)
The culmination of my paper would be Paul's feverish and frenzied riding as if he could be a winner in his mother's eyes if he could just ride a little more: which ultimately causes the boy's death. Descriptions of this section of the story (Paul's actions) will be most important in making your argument regarding "style." Don't forget to incorporate the last line of the story just before you write your conclusion—in a separate paragraph.
My God, Hester, you're eighty-thousand to the good, and a poor devil of a son to the bad. But, poor devil, poor devil, he's best gone out of a life where he rides his rocking-horse to find a winner.
It is important, I believe, to quote passages that show the characters' sense of urgency, shared through the author's careful construction of the story and descriptions. For each general statement, make sure you have a specific detail to support it from the story. Use quotation marks ("_").
Read the story twice, highlighting whatever part you think will support your thesis. Then write your paper, proofread it, and take a break. Go back and read it again, making changes as needed. Take a short break, and read it again, so that you can study it with fresh eyes. Use the grammar and spell-check on your computer. Print out a rough copy so that if your computer crashes (God forbid), you haven't lost everything. And save, save, save!