Always have a .doc (Microsoft Word) format and .txt format of your resume with you. When you are filling your resume in websites, you need the text format and when you are sending resume through mail, it's better to send the .doc format.
Few companies may ask specifically for .rtf format. In such case, you don't have an option anyway.
Try to see to it that the .doc resume file size is less than 100 KB.
Resume File Name
Don't give some junk names as file name for the resume. If you keep use junk names, there is every possibility that your mail will travel to bulk/trash folder of recruiter. Your resume's file name should ideally denote your name, experience, technology, years of experience and company name. Keep some valid name for your resume.
Example: Resume_Riya_J2EE_3 Years_INFOSYS.doc
Example: Resume_Suresh_FRESHER_B Tech_Computers.doc
Exclusive Mail IDs
Use only one (or maximum of 2) mail Ids exclusively for the purpose of recruitments. Do NOT use those mail Ids for any other purpose (Especially you should not use it for subscribing to any GROUP mails or FORWARD mails).
Standard Mail Service Providers
You must be careful about the service providers in which you open a mail account. Don't use the mail Ids/accounts from non-standard service providers. If they disconnect services suddenly, your mail ID fails and you need to resend resumes with new mail Id to all the companies you have already applied. So, always try to create mail Ids with standard service providers like Yahoo, Rediff, Google etc.
Choose both mail Ids from different mail service providers. In case, if one service provider experiences technical problems, you can use the other service provider.
Always see to it that at least 50 % of your mailbox size is free. Delete unnecessary mails periodically.
Send from same mail ID
While sending the resume, preferably send it from the mail ID you have mentioned in your resume.
Always keep a copy
While sending the resume, always keep a CC/BCC to your mail ID (or at least keep your sent items ON) so that you will know whether the resume is attached properly and/or whether it's traveling to bulk mail folder.
If the company mentions that a specific 'Job Code' has to be written in Subject Line, write that. If nothing specific, then give a proper subject line for your mail.
Example: Resume - J2EE - 3 Years Experience - INFOSYS - Bangalore
Always try to include a "short" covering letter just containing your experience, current location, contact details (address & phone number) current company name, technology you are working in. Don't write too long covering letters. No HR will spend time on reading your long letters.
Short is Sweet
Don't make the resume too long. Keep it short & sweet. It should be less than 3 pages (and up to a maximum of 4). The HR will hardly have 1 minute to glance at your resume. He won't have the time to read story-like resume. So, be precise, clear and straight to the point.
Better use bullets for mentioning important points.
Check BULK mail folder
Check the BULK mail folder before blindly emptying it. I have seen people who lost call letters because of it.