Assuming you have done well in school and made yourself a well-rounded candidate with close faculty relationships, you should begin in your junior year to:
Start with Peterson's Guide to Graduate Programs in the Humanities and Social Sciences. Check in your department, the library, and the IUP Career Development Center for further information and catalogs. Call or write for catalogs from schools that interest you. Look especially for programs which match your interests: If you want to study American Literature, look for a program that is strong in that particular area. Remember that school ratings for individual graduate programs are not the same as a school's overall or undergraduate rating. Look for a strong graduate program in your field.
An equally important source is people. The back of the IUP catalog lists the graduate programs from which IUP faculty have received their degrees. Talk to people who have graduated from schools that interest you. If your department maintains a list of alumni, check this to see who has recently attended graduate school, then call or write these alumni, who will usually be very happy to share their experiences and suggestions.
The Graduate Record Exam and the Subject tests in your area of specialization are required by most schools. Look carefully at deadlines and the time it will take for GRE to report your test scores.
Many students find that taking both the general and subject tests on the same day is exhausting and leads to poor scores. They recommend that you take the subject test on a different date.
Applications and specifics are available in the Career Development Center.
Make sure you have some courses on your transcript during the junior year which will be perceived as very solid. In some departments which offer graduate courses, such as English, it is possible for an undergraduate to take up to two graduate courses with permission.
One way to do this is by attending a professional conference in your field of interest. Ask a trusted professor for recommendations of which conferences it might be fruitful for an undergraduate to attend. Go to sessions in which people from prospective schools are giving papers. Later you can write a note saying how much you enjoyed the paper and perhaps even share a bit of correspondence with an interesting professional.
Such an elaborate strategy was unnecessary a decade ago but is fairly common practice among savvy students now. Many graduate applications even have a space that asks for names of any faculty on their staff you have been corresponding with. This procedure won't work if you wait until a few weeks before applications are due; it requires advance planning.