When communicating with others you need to take into the account the information you are sharing, who with and when.
Verbal communication is the mostly used form of exchange but many factors can affect this. It will also change depending on if you are talking face to face or over the telephone for example. When talking your tone of voice and facial expression can express more than the actual words you are using. If you are telling a person you are happy with something they have achieved but frowning at them you are sending a mixed message. On the telephone a person does not have a visual image to read meaning they rely on your tone of voice and the speed of your speech and response. When face to face having eye contact with the person you are talking to helps to show you are attentive and also keep their attention although some may find this unnerving. Your posture and hand gestures will tell the person a lot about how you feel and what you are trying to convey, sitting with your arms and legs folded gives a very closed impression to the other person showing you as being uninterested.. The environment that you are in can also affect your communication; a room with lots of background noise is not conducive to an important meeting or discussion.
It is also vital that you actively listen to the other person, let them finish before you answer and use their words in your response so they know you understand.
If you are using visual communication like sign language, lip reading or even visual aids you need to make sure these are clear and direct. When a person is signing or lip reading they will need to be looking at you and may have no hearing at all. This means you would need to gain their attention in an appropriate manner, possibly by touch. Visual signs like notices/labels need to be designed for a specific age group, for example using pictures instead of words for young children.
People also communicate in written form, like letters, cards, information...