This may seem obvious, but I am constantly amazed by how many spelling and grammatical errors I see in emails from applicants, in their résumés and even on their actual portfolio work. This is a huge testament to your attention to detail. If you don't take the time to proofread a one-paragraph email to a potential employer, what does that say about your work on a daily basis?
It’s pretty apparent to an employer when they receive a generic email that a designer has blanketed the city with in search for a job. Do your research and let the company know what compelled you to apply there above all other agencies. If you get called in for an interview, be on time, know who you are meeting with and don’t forget their names. Tell them why you are excited about this potential opportunity.
I’m sure that your life story is amazing, but most creative directors will not have the time to read through this. When reaching out to an agency, tell them why you want the job, why you are so much more awesome than the next designer, and then prove it with an attached portfolio or link to your portfolio site.
This is the industry that will in fact judge a book by its cover. It is truly important to put your best pieces at the beginning as well as the end to make the best impression. You should have eight to 10 of your strongest pieces to demonstrate that you consistently do work of a higher caliber. In addition, your résumé should always accompany your portfolio and receive the same amount of attention from you as any other design project. Everything you send to a potential employer will shape their perception of you as a designer.
This may well be the most important tip of all. Oklahoma City in particular has a tight-knit community of designers. If you don’t play well with others, potential employers will likely learn this from someone who knows you or has at least heard your name. Talent will only take you so far, and creative directors search for designers who take criticism well and are willing to grow. Even the most talented designers have room for improvement.