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.
Before writing a resume, you should spend time find out carefully about the employer. The more you know about the job and the company, the more suitable your resume and resume may be to the job requirements and as a result, the more your chance will be.