Most of the time, when writing for a client, I have occasion in future posts to link back to older posts. To facilitate that, it’s a good idea to record post titles and URLs for every blog post or webpage that you write, whether for yourself or a client.
Use a simple Excel spreadsheet on your computer. In addition to a column each for post “title” and “URL”, keep a column containing either a short description of the post or keywords, for reference. It’ll help you quickly decide whether or not you want to link to it.
I don’t recommend a web-based spreadsheet such as ZohoSheet, in case you temporarily don’t have Internet access but need link info for an blog post you’re working on.