Take more English classes than your concentration requires. You need to show an admissions board that you have a broad understanding of literature, as well as some knowledge of literary theory.
Study a language, whether or not it is required for your undergraduate degree. Most English doctoral programs require fluency in at least one foreign language.
Form relationships with English professors at your college. If possible, take more than one class with professors whose focus interests you.
Prepare a writing sample to send in with your applications. Ideally, you want to complete an independent study under one of those professors with whom you formed a relationship. Alternately, English honors programs usually require an undergraduate thesis. You need a twenty page paper that proves you can research and defend a compelling topic.
Line up your letters of recommendation. Discuss this with your professors a full four months before you plan to apply. If your hopes for a good recommendation fall through, you will still have time to look for other options.
Take your GRE's the summer before you plan on applying, if not sooner. If your scores aren't as high as you would like, don't despair; study more and try again.
Research prospective English doctoral programs. You can find application procedures, program requirements and funding options on a college's website. It is equally important that you research a program's academic focus. If a department has several professors who share your interests, the school might be a good fit.
Write your personal statement, and remember to proofread. When applying to an English doctoral program, your personal statement should be an impeccable read. Take the time to really agonize over it. Think about topics that interest you and illuminate them with clarity and erudition.