Plans that fit your needs
Ask for instructions in writing
Verbal instructions are easy to misremember, especially for tasks with several steps. A short message asking for a written version, in the format that works for you, is usually easy for the other person to answer.
Reviewing your written instructions request
The draft should name the task so the recipient knows exactly what to write up. "Instructions for the thing we discussed" will get a vague answer. It doesn't need to explain your personal reasons unless you want it to. Ask for a specific format, such as numbered steps or a checklist, rather than "something easy to follow." Check that it asks for a named contact, since instructions are less useful when no one can answer questions about them.
When the instructions arrive
Read them once before you need them, and flag anything unclear while there's still time to ask. If a step seems missing or two seem merged, send a quick reply. Keep the written version somewhere easy to find so you aren't searching for it partway through the task.