Use a writing inbox for friction-free capturing
Maintain some kind of inbox as the first point of capture for notes and ideas. This helps to close open loops. This is the input point for all information that may or may not eventually end up in the Zettelkasten.
On a regular basis, the inbox should be reviewed and the notes taken formed into permanent entries in the note system. If something in the inbox is not relevant, then it can be discarded.