Starting any business has a price, so you need to determine how you're going to cover those costs. Do you have the means to fund your startup, or will you need to borrow money? If you're planning to leave your current job to focus on your business, do you have money put away to support yourself until you start making a profit? Find out how much you're going to need.
Double check yourself, before you double wreck yourself. Make sure everything you send to a company, whether a résumé, an email or a portfolio, is good to go. Double check your grammar and wording, and for God’s sake use spell check! This is especially important when it comes to the company’s name. Don’t spell their name wrong and be sure to type it how they type it (e.g. Problogger, not Pro Blogger).