Truth be told it's hard not to feel uncertain when interacting with someone who is either mentally or physically disabled. It's human nature to approach them with a feeling of pity as we look at them being in a sad state. But how do we create for them a conducive atmosphere in which they feel comfortable and are able to freely express themselves just like we do in public.
Respect is vital for a disabled person to feel important and not less of a human. Despite their impairment these people think and work just as much as we do. Approach them the way you would approach anyone else on any given day to make them forget they are disabled. Avoiding terms that remind them of what they are facing will play a big role in letting them bond in with everyone else.
And as much as the disabled hate being addressed by their condition, they feel offended when they are talked down to. The use specific vocabulary when talking to them, gestures like tapping them and any other ways of showing sympathy make them feel out of place and different from other people. Try to equate them to everyone else without any sign of sympathy to make them feel understood whenever they take a specific action.