Writing an effective cover letter is the first step to get a job. If your cover letter describes you well in the shortest possible way, your chances to get the job increase by 50%.
Effective cover persuades the recruiter to go through your complete resume. At this point if your resume is appealing and finely tuned, that's the point you are eligible for the job.
I can write a perfect cover and resume for you which will be consisting 1 page each, but it will effectively describe you, your skills and your work experience. It simply will be a shortest career demonstration report that will strike the eyes of recruiters of any company.