If you do not know where to start, and you are not familiar with the schools in the area.
Phone the primary schools that are in you area - ask them which are their feeder schools or where the kids who come to the primary school usually come from.
This will give you a minimum of three schools to start with. That way you visit those schools and while you are there ask them if they can recommend others schools in the area and so on.
Try and purchase Jo'burg Child which is a good kid's magazine, has lots of advertisers, and usually the end of year editions cover schools and parties and are a great source of where to start.
You also though need to be realistic that if you are looking for a school now for January, odds are they will be full. Schools usually sort out their enrollment for the January, in the June of the previous year.
But get on to lists, and find a few that you like - and try to familiarise yourself with what you need to do to get enrolled.