Whether you choose to present a single sample of your writing or create a portfolio of several pieces, think carefully about your choice and the way you present it.
Choose something related to the internship or job for which you are applying. Try to match the topic and type of writing to the job situation.
Present a clean, corrected text. Remove any comments or grades from your instructor. Fix any problems you are aware of so that the sample shows your best work. Run the spell checker and proofread very carefully.
Make your sample look professional. If you have not already done so, design the document with ample margins, headings, and a header and footer. Make sure you are identified as the author, and make sure the sample has a date.
Provide some context in a cover letter: Where did you write this? What was the assignment or work setting in which you produced it? What does it show about your skills? What are you proud of in this document?