Try to avoid standing in front of windows or other light sources. The glare from behind you makes it difficult to read lips and other facial expressions. Do not hesitate to ask the student to repeat if you do not understand. If that doesn't work, then use a pen and paper. If a student is using an interpreter, speak directly to the student, not the interpreter.
Short sentences are easier to understand than longer sentences with several clauses.
If the student doesn't understand, try repeating, and if the student still doesn't understand, rephrase a thought or use a different word order rather than again repeating the same words. You will become accustomed to each other in time. It is impossible to lip-read a word that the student has never seen before. If time permits, it helps to write the word and then let him see how it looks on the lips. Facial expressions, gestures and other body language help convey the message.