The many wrong things that I very often see – and that I hope you won’t do.
Ask the development agency for a quote, without having first designed the site’s functionality.
He has internal staff, marketing or whoever write the copy, instead of investing in the figure of the copywriter (very important).
Do online marketing, invest money, and not have an ad hoc landing page with a single main objective.
A website without data collected on Google Analytics (for example) and related economic metrics configured
Redesign the site because it is old, with no browsing behavior data available.
Evaluate the quality of the site, following your own point of view and not listening to what visitors who don’t buy think.
Investing a lot of time and resources on useless site features that no one uses or that doesn’t generate revenue for you.
To be continued.