tldr: think about what you want and ask for it
I get asked for startup advice many times everyday from both YC companies and non-YC companies. I have a limited set of experiences as a startup founder and investor but I am always happy to help motivated founders whenever I can.
The problem is that many founders ask for advice in strange ways. They email requesting to meet for coffee, take me to dinner, give me an update, provide me with background, just get to know me, send me their pitch deck, etc. Basically everything but ask for advice. Now I understand why this is because I used to do the same thing (and sometimes still do). But I have started to realize there is a much better way.
Just send an email that can be read in 30 seconds or less and ask for the advice you want. As a former founder, my instinct is to be a problem solver. With just a tiny bit of background and your question, my brain immediately starts thinking about a solution. Often times when I read emails like this, I can't help but answer them immediately (either with my advice or with a clarifying question or two).
When I don't receive this type of email, I still want to help but its much harder and I'm a lot slower to respond.
So the next time you want some advice from anyone, just send them a short email and ask. It will save you time, save the person you're emailing time, and more likely than not get you the advice you need.