How can a blind, deaf, or deaf-blind person know I'm here?
Blind, deaf, and deaf-blind people have many ways of being able to tell when someone is in their presence, so it shouldn't come as a surprise to you if a deaf/blind person reacts to your arrival.
For blind people, a blind person can hear your footsteps, anything shaking around in your bag. For deaf people, they may be able to feel your footsteps in the floor if you're coming from behind. They may also see you coming in a shadow on the wall or in the reflection of an object. For deaf-blind people, as well as deaf, or blind, people, they may be able to smell your cologne, feel the wind of you passing by, or sometimes just feel your presence. The same way many people can feel someone staring at them from behind works for some deaf/blind people, who can sometimes just feel the presence of another person.
Some deaf or blind people are more sensitive than others, so while some deaf/blind people may be able to tell you've arrived, others may not be able to tell and may need to have you let them know of your presence. Many people can tell in some situations and not others, and for many people it's simply a factor of how focused or distracted they are. It's always nice to inform a deaf, blind, or deaf-blind person that you are leaving or have come back because a deaf/blind might not always realize you left or came back.
How do I guide a blind or deaf-blind person?
Before guiding a blind or deaf-blind person, ask if they want to be guided first. If they do, then you can let them take your arm and guide them. Make sure to factor both yourself and them when moving around objects. Always offer your arm to the side that isn't holding a cane or guide-dog harness.
If the blind or deaf-blind person isn't using their cane or guide dog, it's useful to inform them of changes in terrain, such as curbs, hills, drops, when stairs begin, end, when you've arrived at an elevator, or when you're getting ready to make a right or left turn. If they are using their cane or guide dog, it's not necessarily to inform them of these changes because they're already getting this information from their cane or guide dog. While it's more common for blind people to take your arm, some deaf-blind people might want to take your hand if you are also using tactile sign language. Let them decide where to hold you.
When passing through narrow areas, extend your arm behind you. Most blind or deaf-blind people know to take this as a cue for single-file and will follow directly behind you. A significantly taller blind or deaf-blind person can also put their hand on your shoulder, and a significantly shorter blind or deaf-blind person can take your hand instead of your arm.