Generally students email professors in  applying process to increase chances of admissions or express their research/subject interestes. Contacting Professors could indirectly help student to get Research/Teaching Assistantships. Here is an article by USNEWS which could help in emailing professors.

Professors, like everyone else, have gone electronic. In addition to the one-on-one office hour, they're quite willing to communicate by e-mail. Here are some things to consider before clicking the "Send" button:

1. E-mail is forever. Once you send it off, you can't get it back. Once your professor has it, he or she owns it and can save it or, in the worst case, forward it onto colleagues for a good laugh—at your expense.

2. E-mail goes where it's told. Check—and double check—to see that the right address appears in the "To" line. Just because your mom and your professor are both named "Lynn" is no reason to send all your love to Professor Lynn.

3. Professors might not be using the cruddy university e-mail system. So send it to the address they actually use, not the one on the university directory. (Check the syllabus or assignment sheet for clues.)

4. Professors might not open mail sent from luckydogpig@thepound.com. They prefer to open mail sent from more reputable addresses, like you@theCruddyUniversityE-mailSystem.edu.

5. Subject lines are for subjects. Put a brief explanation of the nature of the e-mail (like "question about paper") in the subject line. Never include demands such as "urgent request—immediate response needed." That's the surest way to get your request trashed.

6. Salutations matter. The safest way to start is with "Dear Professor So and So" (using their last name). That way you won't be getting into the issue of whether the prof has a Ph.D. or not, and you won't seem sexist when you address your female-professor as "Ms." or, worse yet, "Mrs. This and That."

7. Clear and concise is best. Your prof might get 25 or 30 E-mails a day, so, it's best if you ask your questions in as focused and succinct a way as possible. (Hint: it's often good to number your questions). And, if your question is very elaborate or multifaceted, it's best to go to an in-person office hour. You'll get better service that way.

Extra Pointer. Before sending a draft of a paper to a professor as an attachment, check to see that he or she is willing to accept such longer documents. If not, see if he or she will look over a page or even a central paragraph of your work incorporated into the body of the E-mail. And be sure to "cc" yourself any time you send a piece of work; who knows the fate of the copy you're sending?

5-Star Tip. Never e-mail your paper as an attachment in a bizarre format. You might think that .odt is really cool since you didn't have to pay for Open Office. But what when the professor discovers it takes him or her 20 minutes to find the plug-in that doesn't work, then another half hour to download Open Office (which ties up all too much space on his computer). What was supposed to be a 15-minute grading job on your paper is now taking over an hour. And then the prof has to assign your grade? Stick to Word.

8. Always acknowledge. If your professor deigns to answer—or send you the handout or reference that you asked for—be sure to tell him or her that you got it. That way he or she will think kindly of you next time they see you in class.

9. THIS IS NOT A SHOUTING MATCH. Don't write in all uppercase letters, which is an E-mail convention for anger or other strong emotions. No one likes yelling.

10. No one really likes emoticons and smileys. Trust us on this one. :)

11. This is not Facebook. Don't write the professor in the way you'd write on your friend's wall.

5-Star Tip. It's never a good idea to "poke" your professor, no matter how funny it seems at the time.

12. This is not IM-ing. So pls dun wrte yor profeSR lIk ur txtN. uz abbrz @ yor own rsk. coRec me f Im wrng. (Translation thanks to www.transl8it.com, which features a neat little Facebook widget.)

13. This is not CollegeHumor. Resist the temptation to talk about the "bad ass" paper you need help with, your "loser" TA who didn't teach you what you needed to know, or the "crappy" grade you just got on the midterm.

14. This is not RateMyProfessors.com. The professor doesn't want your comments about his or her performance in the class. Save those for the end-of-semester evaluations, where you'll be able to spout off. Anonymously.

15. Spelling mistakes make you look like a doofus. So always use the spel check, and proofread yyour e-mail, two.

16. Signoffs and signatures count. Always end by thanking the professor for his or her time, and closing with "Best wishes" or "Regards" (or some other relatively formal, but friendly, closing). And always sign with your (entire) real name, not some wacky nickname like Ry-Ry or Biff.

17. Your prof doesn't want to hear your philosophy of life. Skip the cute quotes or statements of your religious or political views at the bottom of your E-mail. You never know what offends.

18. Don't lay it on too thick. It's one thing to be polite and friendly in your e-mail; it's another thing to wind up with a brown nose.