Make an impression from the very first email.
99% of applicants don't get past the enquiry stage. Many email applications are deleted due to poor quality. You cannot send emails for job applications using the same casual tone that you use for friends.

Include your name and phone number in the email.
Too many people just include their full name and contact details in the resume. You must include your first and last name, and your phone number in the body of the email itself—so the employer can call you.

Pull your own weight in the job application process and don't expect the employer to do all the work.
Employers don't usually respond to applicants who don't contribute some information about themselves upfront. Take the trouble to say a little about yourself in the body of your email. A few eye-catching points.

Spellcheck your email enquiry/application.
Lazy spelling, grammar and punctuation will show the employer you don't care whether you are considered or not. Watch out for differences in Australian/US spelling. The z/s problem is a common one.

Attach your resume/CV to the email.
An employer has little time to send emails back and forth. Make their job easier by attaching your Resume/CV in the first place. Don't hold back by saying that if they are interested you could send in your resume—this is game-playing and wastes everyone's time.

Consider your job application as an investment in your future.
An employer is looking for more than just someone who can do the job. He/she is looking for someone who will fit into the organisation and actively contribute to the workplace. Demonstrate this in your application. Put some effort into it. Your entire job application is your marketing tool that sells YOU—just like an advertisement would sell a product or service.