These days, almost everything is done electronically, including resumes and cover letters. However, some people like to stand out from the rest by including a handwritten cover letter with their resume. They feel it adds a personal touch that is usually missing from today's job seeker and show their attention to the small details.
Make sure you have neat, clear penmanship. After all, your letter and resume are being held up in comparison to others that have been neatly type. Don't use cursive writing, and be sure that your penmanship is easy to read, as neat as possible and isn't rife with a lot of flourishes or scribble. Write in blue or black ink; avoid red or other fancy colors.
Keep it short, simple and to the point. Don't drone on and on about yourself and your personal experiences in the letter. Just because your letter is handwritten doesn't mean it shouldn't be professional. Start out by introducing yourself, give a paragraph or two (short ones) about your professional abilities, provide contact information and close the letter with a thank you and your signature. You want to sell yourself in just a few paragraphs, so be sure to emphasize the things you do best and make a point to showcase why this company needs you.
If possible, write your cover letter on stationery. It adds a sophisticated touch and gives the personal result you were trying to achieve. Stay away from notebook or computer paper, as that can make your cover letter look sloppy, juvenile and unprofessional. Make sure the stationery you choose has a simple design and is easy to write --- and read. Stationery gives your letter a more polished look and has the appearance of a note from a friend or colleague, which is the feeling you are trying to convey with your handwritten cover letter.
When you are submitting your resume, make sure your letter is paper clipped or placed on top. If you must mail your resume, be sure to take care when folding your letter, or use a 9x12 envelope to avoid folding. After all, you don't want your ink to run or bleed on the paper. Don't staple your letter, because again, this tends to look a bit messy and unprofessional. If you can't paper clip it, then simply place the letter on top of your resume and submit it in a plain folder, with your name clearly written in the tab.