protocols.io is a web-based tool that allows you to write, store and share protocols that you have developed. You can upload incredibly detailed protocols complete with links to reagent suppliers. These protocols can then be shared either within your direct research group, with a select group of collaborators, or broadly on the web.
protocols.io has generated a guide protocol of best practices when writing a protocol. It can be found here. It includes tips for making your protocol more reproducible, discoverable, and user-friendly. I recommend reading this protocol in its entirety before getting started.