What to look for in a flight instructor?
This is an excellent question and at the same time, very broad. Every student and pilot can give you a ton of advice about what qualities the best CFI must have. I will list a few qualities to look for and then guide you to a few resources which can further elaborate the topic.

I presume you are going for Part 61 (14CFR61.159). I also presume that you have selected a flight school or will choose from a few around your.

Once you get to a flight school, normally you will be assigned a CFI by them. They will interview you and you should do the same.


Ask the CFI why they are teaching and what their goals are
Generally speaking, one half of CFIs are doing it for their future career goals (i.e. to get a job in an airline) and others are doing just because they earned the CFI rating and hence are earning money by teaching.
Once you start flying with a CFI, see how they respond to your mistakes
You are a student and are learning something new. There is no way that you will master everything taught just once. (Maybe you can, I'm not just that smart.) Observe how the CFI will notice your mistake, bring it your attention, rectifies it themselves or gives you instructions to do it, and most importantly, how your mistake affects their mood?
Before and after each lesson, notice how they answer your questions and explain to you what you guys will be doing and have done
Some people (like me) would ask a million questions. Often times, you will find teachers/instructors who don't like to be questioned a lot. All your questions are genuine, you just need to see how they are answered.
Ask your pilot friends to guide you, or check with other students at your flight school.
Your friends can give you a very honest feedback. You can benefit from other students too, but if a CFI works for someone else, they may not work for you. You are the one to judge and make the call.


Naturally, you cannot know about a CFI's style unless you take a few lessons with them. That will definitely cost you money. But spending a little money to learn a valuable lesson is not wasting money. It is an investment.

I am not talking about some other details as they are discussed thoroughly in the references below.



Here are some resources which have answered this same question in more detail.


Pilot Tricks
Ask A Flight Instructor
wiki How
AOPA (AOPA has an article about almost everything aviation-related)
About Money
Flying Mag