Ask HN: how do you start high-tech consulting?

Let's say you have half a decade in the industry, you have done startups, and you want to keep fueling that addiction (and putting food on the table) by doing consulting on the side. Just enough to pay the bills, get good ideas from customers, refine one's chops and learn new tricks.

Where do you start? Are there perhaps good guides / resources /books for this?

How do you scope the technologies you'll be working with? Let's say you're familiar with Ruby and its ecosystem and you get a .NET potential contract, do you take it and very quickly learn on someone else's dime, even though you could have done the same 10x faster in your main stack/ecosystem?