Have a normal conversation with them. Do not let their illness fool you into believing that they are any less intelligent. On the contrary, ill people mostly have a higher intelligence than the rest. There is no need to be unnatural and say things that you feel they would like to hear, because they can quite easily tell when someone is lying to them or trying hard not to blame them for something that they are actually guilty of. Be willing to share your opinions with them, while patiently listening to whatever they have to say. Just because they are ill does not mean they do not have the ability to understand and analyse things and situation better than you.
Remain cool and calm while talking to a person with schizophrenia. You do not want them to feel threatened or agitated by your actions and gestures. Understand that paranoia is a major part of their illness and therefore it will take a very little from your end to make them feel unsafe. Therefore, do not stare too much in their eyes, do not raise your voice at them and do not make an assumption that just because they are schizophrenic, you have to treat them differently. Treat them how a human would ideally treat another human, i.e. with respect and love.
Do not talk about their illness with them, at least not until they themselves bring it up. Understand that it is not easy for them to cope with their illness, especially with the people around them treating them as patients. They want to feel and be treated as normal, which is why they avoid talking about their illness. A schizophrenic will most likely be comfortable discussing his condition with his close family and medical team only. You have no right to remind them of their state and therefore should avoid touching this topic with them.
Seek help from a trained mental health specialist immediately when a schizophrenic is having an episode. Try to contact their doctor or psychiatrist if possible. When a schizophrenic starts hallucinating, making threat or accusation, do not engage them yourself. Keep calm and immediately get help. Trained mental health specialists know how to handle a schizophrenic while he is having an episode.