to start set aside a whole day at home, let your child just sit on the potty even if they dont need it straight away. if possible let your toddler wander without a nappie on. every time he/she starts to do anything away from the potty quickly move them onto it. they will quickly pick up the connection between the two. be patient, you will have a few accidents. persiverence is the key. good luck!
Make sure your child gets what's happening and why he's sitting on the potty chair. Later you can ask him(or her) "Do you have to go potty?" Sometimes it's better to wait a little longer. When your kid wakes up in the morning check his diaper. Being dry is a sign that he's ready to start.