Picking a reader takes more than handing your manuscript off to the next person you see. A reader can be instrumental in the success of your writing so choose carefully.
First, you need someone who is an avid recreational reader. The higher the book count the better because he won't differentiate between your manuscript and the book he just bought today. Someone who reads in multiple genres and mediums is good too, such as mainstream fiction, magazines and the daily newspaper. This person knows what sits on the store shelves and can evaluate how your work will play within the current trends.
Second, an effective reader can explain the reasoning behind his opinions. How many times have you handed a manuscript to someone and only to have the person say, “Oh I like it “ or “It’s not my favorite”? That doesn’t help when you're trying to figure out if the ending gives the payoff promised or simply stops the story. There must be some give and take with both sides questioning each other. You have to feel comfortable with your reader to ask why does he think that and to play a game of "what if..." with him.
Third, honesty is the most important issue in the writer-reader relationship. The risk of hurting your feelings may keep the people closest to you from giving you an honest critique. Ask yourself, "I can trust him with my life, but can I trust him with my manuscript?" On the flipside, struggling through life together can strip away all pretenses making your soulmate or your best friend the perfect reader. He knows you and how you work and you know him. Any inkling of sugar-coating would be spotted right away. As your friend, he wouldn't betray the trust you placed in him when you turned over your manuscript.
Next you need to decide if a reader is necessary for you. Look at your limitations. I have a hard time seeing simple mistakes, not only in my work but in whatever I read. My mind automatically corrects the mistake and I read through it. Readers can spot basic errors and typos because they read with fresh eyes. They can tell you what works, what to fix and what to cut out.
I also have a habit of "writing short" for the sake of the word count, sometimes sacrificing clarity. When you research a project, you learn far more than you'll ever put in your manuscript. As a result, you may leave out information inadvertently because you know what you're talking about. You know the backstory. A reader can point out areas where your 1000 words don't add up to a picture for those outside your brain, and he can work with you to get your point across without busting the word count.
It may be that you'll find a need for more than one reader. Different people give different perspectives even when they're looking at the same manuscript. Life experiences, interests and education all influence how a person looks at the written word. Two people may like the same things but for different reasons. They may pick out the same problem area, but offer differing solutions. Of course, you could get critiques that make you wonder if you even gave them the same manuscript. In any case, they'll both give you something to think about.
If you write in different mediums, it can be helpful to have different readers for each. A reader who enjoys fiction might find nonfiction boring, while a nonfiction reader might not pick up on the nuances and subtleties of fiction. Another way to split your reading needs is between grammar and content. One can read for sentence structure, grammar errors and spelling, much like a copy editor, while the other handles the big picture of content and flow. Then there's the availability issue. If your deadline looms and your reader is on vacation, having a second reader available saves you that risk of submitting a flawed manuscript.
Deciding on the need for a reader is personal. If you're already selling every word you write, you might not need a reader. If your sales are sporadic or if you find yourself bogged down in revisions unable to let anything go, an effective reader can help. So evaluate your career honestly, recognize recurring problems, then look for someone with the traits and skills to give your next manuscript a good read.