Mobility impairments can vary from not being able to walk through to using a wheelchair or powerchair, to being able to walk short distances or with the support of a mobility aid such as walking stick, crutches or walking frame. www.scope.org.uk
Always introduce yourself.
Speak directly to the person.
If the person uses a mobility aid ask if they would like a seat.
Ask permission before touching the person's wheelchair or mobility aid.
Offer to carry items if required or bring things to the person.
If you are having a lengthy conversation with a wheelchair user find a seat and sit down.