Make your resume and resume differ from those of other candidates. As such, you should never start your resume with such general salutations as dear sir, or dear sir. Normally, when a company posts publicly a recruitment ad, it will surely address the name, address and contact number so as the resumes may be sent to correct address.
Check spelling and grammatical errors: Even the smallest spelling or grammatical error may become the reason that eliminates your name out of the list of potential candidates. So, do not forget to check carefully for any error before clicking the send button, or bringing the resume across a long way to the employer.