For example, what is the proper way to deal with someone with Down syndrome or someone in a wheel chair?

I always get really awkward, and I don’t know what to do.

I feel like If you look at them, you are being rude and staring, but if you don’t look at them, you are ignoring them and pretending they don’t exist.
I feel like it’s a lose, lose situation.

Does anyone have any suggestions?