All of these comments are great. Other tips on selecting a patent attorney:
At a minimum, your prospective attorney should quickly be able to parrot back, in his/her own words, what your invention is accomplishing. That helps show the attorney understands it. But even better if they are taking your concept and pushing its limits -- asking you about other potential use cases, other ways of implementing the invention and variations on your idea. When you are working REALLY well with a patent attorney, they're not just a scribe. They should be pushing your thinking about what the invention really is. This helps ensure you are capturing the full potential of the idea in the patent process.
Also, you may want to look for somebody who focuses on working with startups and growth-stage businesses. Aside from drafting a quality application, there are a lot of strategic decisions involved in building a patent portfolio. And the best course of action will often be completely opposite for a Fortune 500 company versus a startup. Which means there are a lot of really bright attorneys drafting high quality patent applications, who would NOT be the best choice of counsel for a seed-stage startup. Talk to your prospective attorney about where your business is right now, and where you see it going. Do they understand the stages your business is going through in terms of product development and achieving product-market fit, competitive landscape, evolution of your market, capitalization, investor priorities, etc.? The patent strategy may evolve over time, but a patent attorney that is savvy in your technology and business stage should be able to very quickly articulate a patent strategy that aligns well with your broader business strategy.
Lastly, re: the idea of trying to draft the body of the patent application before you meet with an attorney: this can be very beneficial if you can and want to invest the time to study a lot of patent applications and get a feel for how they are drafted. Otherwise if you don't want to invest time in learning how patents are drafted, focus on drawings. If you can sketch out flow charts and block diagrams that illustrate your invention, it's relatively quick/easy for a good patent attorney to put the right words around it. The hard part is figuring out the best way to conceptually convey the invention in the first place. Good illustrations from an inventor can help immensely.