No Freestyling, no Feature-creep.
One excellent reference I can point you to, is this book by Daniel Kahneman, Thinking Fast and Slow
Just reading a few pages will ensure you’ll not allow easy-to-recall, duff facts or ‘guru’ opinions to get in the way of the job your website has to do.
My methodology, is that good design and function come from refining and rationalising rather than adding whatever someone else said worked on someone else’s business site.
Your project is unique, but it will be constructed with tried and tested modules, formulae and best-practice. The creativity I bring is in purely sticking those bytes together in the best possible way to generate profit for all involved.