1. How you address your cover letter. Job applicants often spend time trying to hunt down the name of the hiring manager so they can address the letter to "Dear Ms. Smith" rather than "Dear hiring manager." Most managers don't care at all if you took the trouble to find their names. If it's not readily available, "Dear hiring manager" is just fine.
2. Your resume design. What employers want from your resume design is a document that's clean and uncluttered, easy to scan, not overly fancy, and puts the information we want in the places we expect to find it. Whatever design you choose that achieves those goals is fine with us.
3. Whether your resume is one page or two. Unless you're right out of school, it's fine for your resume to take up two pages. Consider this license to stop using small fonts and narrow margins to cram everything into one page; we don't mind two (and would prefer to spare our poor strained eyes).
4. Your "personal brand." Employers don't care about your personal brand; we care that you do good work. The evangelists telling you that you must build a unique and recognizable personal brand are looking for a new concept to sell you in an overcrowded marketplace. Employers—the people actually thinking about hiring you—could care less. Do good work and build a good reputation, and forget the branding hype.
5. Whether your post-interview thank-you note is handwritten or emailed. What we care about is the content of the note. Is it well-written? Does it express enthusiasm? Does it build on the conversation we had in the interview? If it does these things, it's done its job. It doesn't matter if it arrives via a handwritten note card or in an email.
6. Your college major and your coursework (in most cases). With some exceptions, employers generally care that you have a degree, but much less about what field it's in. And (again with some exceptions) they really don't care about what classes you took or what you wrote your papers on. They want to know that you attended a reputable school, did well there, and graduated. Beyond that, most of us really care more about work experience.
7. That summer job you got fired from in college. One job that didn't go well isn't going to kill your candidacy. We all made mistakes when we were new to the workforce. As long as you have other work experience, it's not a disaster. In fact, you don't even need to include the job on your resume, although if you do, be prepared to talk about what you learned from the experience.
Alison Green writes the popular Ask a Manager blog, where she dispenses advice on career, job search, and management issues. She's also the co-author of Managing to Change the World: The Nonprofit Manager's Guide to Getting Results, and former chief of staff of a successful nonprofit organization, where she oversaw day-to-day staff management, hiring, firing, and employee development.