For "I don't want these people to have my number" this stuff is fine. Assuming you want a burner phone to defeat state-level agencies it's a little more complex then that.
Best Practices for Burner Phones
Never user your burner at home, work or near your existing phone.
We know that location traces are a thing. You have to assume that if you are buying a burner phone, a state-level agency (police department, FBI, DEA etc) is already interested in surveilling you. If you are like most other people you already have a phone tied to your identity either by the method of payment, name on the account, address or other identifier. If you are like most other people, and you don't want to increase suspicion, you don't turn off your regular phone for long periods of time. If they are tracking your existing phone location (which does not require a warrant) and your Burner is active in the same location, your burner is now connected to your identity, and what ever you do with the burner is now compromised.
Only use cash & be irregular when buying airtime.
The airtime purchases are location and time stamped. if you always buy minutes from the same place or when you buy groceries, there is a point for surveillance to gather information and close the net.
Be sure that the places you are buying minutes from are away from your home and/or workplace.
Never, ever, ever use a card to buy minutes or the phone. If you are in an organization that is using burners (A medical marijuana dispensary that cares about privacy) different members can buy minutes cards and then trade them to confound location information even more.
Activation.
This might be a no-brainer but do not use your personal or work computer to activate the phone, or manage it in any way. Go to the library or other public computer.
Misinformation
Feature phones are still able to be pinpointed to 100', There are really not any more secure then smartphones.
Consider the cheap smartphone, I've seen Moto E phones for less then $20, and they give you the advantage of being able to use TextSecure/Signal (which encrypts SMS and voice end-to-end) and Tor for internet communications.
Personally I find the keyboard and other features faster and easier to use then a feature phone. Of course you need to be sure any accounts you link are pseudonymous and that no other features are tied to you.
Remember to forget your phone.
When using your burner, we mentioned that you don't want to have your usual phone nearby.
While you can turn one off and then turn the other on (hopefully after you've moved and are in a public space with other people), it is better to leave your usual phone on, at home or work. Maybe in the pocket of a friend who is going somewhere else.