Your beta reader is the first person to read your rough draft. This is the person who tells you what scenes work or don’t work. Notifies you of grammar and spelling mistakes. Someone who will be critical and brutally honest. So, whoever you pick as your beta reader is very important. Family and non-writer friends need not apply.
My family are so supportive but never are truly honest. Rather they don’t know enough about the writing process to provide the right honest opinion. My first critique partner was fairly helpful but at the time, I was more productive than he was. While we remain friends, our partnership dissolved. I moved on to an online critique group which I pretty much ran. Had basically the same problem. Since then, I have had writing friends critique my work but not a reliable beta reader.
You must have a set criteria for the beta readers you seek. For example, someone who has a similar work ethic as yourself or writes in the same genre. Be specific as to what kind of partner you are looking for.