I believe, drafting a patent application is somewhat like riding a bicycle, once mastered really never forgotten.
In principle, there are two approaches for drafting a patent application:
Claim based:
Discuss with inventor on the first interview what could be the starting point of a good independent claim (preferably in view of the prior art). Expand this claim as to become the specification.
Specification based:
Discuss with the inventor the structural/functional feature of the invention/device. Draft the specification (thereby understanding the structural/functional features of the invention/device) and then draft the claims (preferably in view of the prior art).
The first approach works better with simple invention/device, the latter with complex invention/device. However, in practice, will be more a combination of the two approaches.

My current patent drafting procedure is that even before I would meet with the inventor, I would ask if he/she could write up a basic write-up, preferably with drawings of the “invention” (device) and send it to me before the meeting.
At the meeting with the inventor, I feel that the best approach is generally to let the inventor describe and draw his invention with all the essential features.
Ask related ancillary question.
– What is the “problem/task” the invention solves?
– How does it solve that problem/task functionally and/or structurally?
– How does it differ what is out there (prior art) functionally and/or structurally? (Was any prior art search performed even if rudimentary? What was found? Duty to disclose.)
– what is the commercial embodiment and what are the possible alternative commercial embodiments (this can be very important for claim drafting), what does the competition use/have?
This first meeting should yield sufficient information for good first draft of:
– Title of the Invention (also often used in the preamble of the claim)
– Background of the Invention (prior art, problems the prior art (competitor) has)
– Summary of the Invention (What does the invention do and/or what problems does the invention solves, concept of the invention, often quite similar to what is stated in the independent claims.)
– Description of the Invention (basic description revised either at the meeting or by the inventor)
– Drawings (drawings by the inventor)
– Claims (from the discussion of the essential features, preferably drafted together with the inventor)
– Abstract (generally, generalized content of the independent claim)

* * * *