An average skilled lipreader may be able to lipread up to 30-35% with a guesswork for the rest of it. That is, missing and misunderstanding words are common. Not all deaf people are lipreaders, many of them none at all.
This video has no sound (hey you, don't you dare to turn the sound icon on, didn't you?). Guess what does the girl say? List as possible words as many as you can guess before you can peek (click on) the answer.
We don't speak one-word sentences in everyday life, right? Read the text below which is what it feels if you were lipreading a few sentences.
"HELLO HOW ARE YOU? LET ME GOT MA PEPPER AD PAN..." or another perhaps better lipreader might interpret it differently: "HELLO HOW ARE YOU? LET ME GET MY [?] AND MAN..." Can you lipread it and do the guesswork?
Answer: "Hello how are you? Let me get my paper and pen." This is simple, but imagine an in-depth conversation and a degree of speed that gets more complex.
Imagine some more possible, confusing term pairs: weather vs whether, elude vs allude, and other uncountable pairs or even trios... in conjunction with other factors such as a drooping moustache. :)
It's not unusual that a "hard of hearing" person prefers one-to-one converations rather than in a group conversation. Many Deaf people prefers "paper and pen" conversation, whether typing on smartphone or writing on paper/digital screen in combination with gestures (like thumb-up, nodding, waving no, etc.).
Nodding away. It's not uncommon that Deaf persons may simply nod and smile to get out of the small talk. Or, simply tired of telling a hearing person to use writing/typing instead. Or, not want to drain a hearing person's patience. Or, if they care, they will ask (gesture) for writing.
For us Deaf people, we prefer our natural language (e.g. ASL) in the same way hearing people vocally speak English or other languages. Next, we prefer communicating by writing/typing back and forth in English for clarity with hearing people who don't speak ASL or other signed languages. For some Deaf, lipreading is used in some circumstances (e.g. one-to-one level rather than in a group) but captioning or interpreting is preferred but also legally required in educational, medical, and legal settings and such when requested.
In public service, ask a deaf person what they prefer or simply follow a deaf person what they do. If they gesture "writing", then grab a paper and pen.
A funny story has been passed around in my time during the 1980s and 1990s, but I don't know if it's a true story. At a restaurant, a deaf person tried to tell a waitress to bring something. She mouthed repeatedly as the hearing waitress couldn't figure out. Unsure of herself, the waitress brought a toilet paper. The deaf person finally resorted to writing on the paper, "salt + pepper".
In late 2007, a hearing male white colleague once asked me a question in our conversation (via typing). He asked, "Can you lipread?" First, out of courtesy, I replied to his question "no" and then asked him, "can you handread ASL?" The hearing man awkwardly giggled, "no."
This question looks at a hierarchical hearing-male-white domination that I don't expect to fit in their world; rather we find a common ground (e.g. writing English back and forth).
Rather than asking a deaf person if they lipread, find out what a deaf person prefers. If a hard-of-hearing person vocally speaks, you can vocally speak. They will tell you to slow down a bit and you can adjust. If a Deaf person gestures "writing", then grab a paper and pen -- don't repeatedly vocally-speak which is annoyingly oppressive (which is not common as most of you are open-minded and well-aware).
If you know a little ASL, Deaf people are delightful, no matter how you think your signing is "bad" to communicate with us. Use it.:) We do appreciate your willing to learn a bit of ASL.