First off, you need to know the contracts, order forms, and payment arrangements involved when working with a factory. It would be good to have a confidentiality agreement to make sure that your designs are not copied by your manufacturer.
Second, you need to be explicit about what you want. Provide as many details as possible such as coloured illustrations and actual swatches. You should provide a tech pack for more comprehensive instructions, and ease of communication. There will be comments on changes and recommendations that need to be diarized so at a glance each person who works on the file has all the answers they need. Tech packs can be hard copies, or shared digitally. There are some fantastic industry specific project management software programs available such as WFX WebPDM that allows users to login and make changes, rather than managing emails and excel sheet update chaos – but there are costs in involved so this may be something you can implement further down the line.