Listening is harder than reading. In reading you can pause to take a break or take notes, start over, read multiple times, and you can mark up the text. If you are doing professional listening on the job, working with clients, or even in class, you have to take the listening up a notch. It is no longer casual listening and simple conversation.
If you are listening to the boss, client, or a peer about a task, project, or expectations, it is important to hear and understand the key bits. It is also important for the speaker to know that you are indeed listening, got it, understand it, and can proceed with whatever is being talked about. Often this means making and keeping eye contact, giving verbal or non-verbal feedback (e.g., nodding of the head) at key points. You cannot zone out and think about other things.
Do some preparation in advance if you have to - it will reduce stumbling, help you concentrate on what is being said, and allow you to look bright, engaged, and smart
Anticipate what the conversation is about and do some homework, research, thinking in advance; so that while there will be some surprises, you are not 100% clueless.
Anticipate questions you might want to ask.
Anticipate answers to questions you might have to answer.
Listen for any adjectives and phrases used - what is being emphasized, the type of emphasis - e.g., most people, really expensive.
Many of the points above came from a workshop for actors on how to read and understand Shakespeare - the actor needs to interpret and understand what Shakespeare intended - the emotion, the body language, the speed of speech, etc. The actors are taught to look for sequences, at the adjectives, etc.
Shakespeare does not tell you what is funny, happy, sad, ironic, monumental, or sarcastic, you have to figure it out. This is the same with listening. It all comes down to the words and the patterns of words. Not all words are important. You want to hear and understand the words you should hear and understand.