Before we begin, I feel it's crucial for me to point out that people who are visually impaired are still people and their condition is just a part of who they are, the key word here is 'person' not 'blind'. So you do not need to modify your behavior much and should not treat them very differently than you would any other person.
Now, when meeting somebody who is visually impaired, it is better to get your presence acknowledged right away. Make the first move, go say hi! Let them know that you are around them and are open and willing to talk. Clichés like "Do you come around here often" or "How do you like the weather today?" work just fine to break the ice and get the conversation going, just like it would with anybody.
Do Introduce yourself and make it a little elaborate; things like friends in common, prior encounter(s) with them, if any, are worth mentioning so it becomes easy for them to place you and feel some familiarity and commonality. If there are others involved in this conversation with you let them introduce themselves and encourage them to give a brief description and the nature of their relationship with the person in question and refer to people by their names so as to benefit those who can't see who one is talking to.
Do not talk to them through somebody else, do not address questions or statements meant for them to people who happen to be accompanying them (their spouse, tutor or a friend, etc.) because that might make things less uncomfortable for you, but you are putting the others in a tough spot as this is a very difficult situation to manoeuver. Instead, let them be an advocate for themselves, talk to them directly!
Do not scream, shout/talk slowly or feel like you have to modify how you speak in any way. Most visually impaired have perfect listening capabilities and even if they are unable to comprehend you for some reason, they are going to let you know. One should avoid situations where competing noise is an element as it can cause hindrances while interacting with them.
Do not feel like you have to modify your speech to omit words that refer to seeing so as to not offend them. Phrases like "look at that" or "watched that movie" are an active part of our everyday language and the visually impaired use them too. If they are able to tell that you are trying to avoid phrases such as these on purpose, it may give you an air of inauthenticity. It's best to keep things natural; you do not need to try too hard!
You should also continue to use your body language as it has a considerable impact on the tone of your voice and how you speak and in addition to providing the unsighted with extra information, it is going to help you to remain genuine.
It is very important to remember not to touch or grab them or their things, do not try to grab their cane and try guiding them with it in order to assist them. If it seems to you like they might require help, ask them first. Do not attempt to help unless they accept your offer. It is possible that they refuse your help and there is nothing personal about that. The impaired are still physically able and have gotten the hang of doing things without seeing and in the spirit of independence like to do things for themselves. Some also have partial vision and are able to function well enough.
But if they do ask you to help them, make it a point to be tender. Do not push or shove, ask them to take either your hand or your elbow (give them an option). Do not scream directions or clap, be polite and as you guide them, describe what is around them and give proper directions. When you are done assisting them, have gotten them where they need to be, it is best to have them get familiar with the surroundings, let them know what is around them, guide their hands towards those objects, things like walls, tables, chairs make people feel more familiar with a room.
It is important to note that concepts like 'over there' 'this' or 'that' are abstract to them. When referring to things or giving them directions, its best to be clear and concise. For example, when guiding them, tell them they have to walk about 7 feet and then take the first right even if they have taken your hand or elbow just so they feel more comfortable. If they have asked you for directions to someplace or something telling them "it's over there" is no help at all. Be prompt, not vague with your directions. When describing a thing, do not say 'that', use definitive terms, name the thing and describe if needed.
They can tell when you are on the phone or not paying attention by the pauses in interaction or by the senses they have developed over time as they have led lives without eyesight and will be able to tell a person is not putting in the effort anymore. In this sense, this interaction is just like any other social interaction and you need to be present and authentic.
It is of the utmost importance to remember to let them know when you are leaving or even moving away for a while. They deserve a proper parting and should not be left talking to the air.