I am not very good at asking for help. For example, before I have someone read something for style, I have already revised it to a point that there are not a lot of stylistic suggestions left to be made. I don't believe in showing a "rough draft" to anyone else. What I like to do, however, is to consult with people in my field without wasting too much of their time. So I wait until I have a significant question or two. I almost always say yes when someone else consults with me in a similar way; that way I accumulate good will and have people I've done large and small favors for. I never do this at the last moment, when I need an urgent answer within less than a week.
Today I sent two paragraphs of my introduction to my current project to 4 people, all of whom would be predisposed to help me for various reasons.
Some requests for help are ways of saying: let's have a dialogue, I want to be talking to you about my project. In some cases, the question you are asking is kind of a pretext. Most people will welcome serious interlocutors. If they don't, they are jerks.