Are you a good writer? Are your presentations interesting and effective? How do you know whether what you have written or presented is good or bad?
Sometimes you will receive unsolicited comments from your boss or a colleague but often all you will get are some suggested edits to your draft. If done well I suppose you could learn from the edits but often there is no explanation of why the change is being made. Was your favourite sentence or paragraph cut because it was irrelevant, badly worded, repetitious or just too long?
What you need to get better is proper, constructive criticism. You need someone who can explain where your writing (or presenting) can be improved AND how to improve it. The only way to get that is to ask for feedback from someone you trust who you think is better than you at writing/presenting.
Except I am saying DO NOT ASK FOR FEEDBACK. Instead, ask for advice. Saying to your boss, colleague, friend, whoever, “can you give me some advice on how to improve [this report/letter/email/presentation/etc]” is a positive start to a conversation.
Not only is it more positive in tone, I have found it works better. At the end of teaching a class, when I ask the class for advice they are more willing to talk to me than when I ask for feedback.
I think this works in an office setting, too. If you ask for advice your colleague can approach it as helping you. And if you are in a leadership role then you get two benefits. First, there is more chance of a member of your team saying something useful if you ask for advice on how to improve something because no-one likes to criticise their boss directly. Secondly, you are modelling a positive behaviour for your team to adopt.
I recommend you give this tip a try next time you are writing something and want the input from somebody else. (And feel free to get in touch with me if you would like my advice on how to improve what you have written.)