In reply to s3lene.

Days are individually self-indexed by date (one card per day).

I'll often keep fleeting notes of random things throughout the day, but later I'll flesh them out more fully and move them to either my commonplace book or to my zettelkasten where I build on knowledge of subjects over time.

I keep some traditional monthly trackers on gridded cards which I put at the beginning of each month, so that's always easy to find.

If I want to track things like doctor's visits for health (for example), then I've got a specific section for "Health" information. It may be scribbled on an individual day, but I'll usually cross index it to my Health section at the end of the day or week when I'm doing my planning.

I usually have a multipen with me (Pilot Hi-Tec C Coleto, pictured), so appointments are usually in blue, to do items in orange, notes of things that will need to be transferred or cross-indexed in purple, and journaling about impressions of today in black. Both the color and the location on the card usually make it a lot easier to find almost anything.

My drawers of files are broadly split up into broad sections:

Bullet Journal (by year, month and date),
Rolodex (usual names, addresses, notes on people/companies),
General information (by category title; things like the health example above),
Projects,
Zettelkasten w/ subject Index (for all the rest of my information, most of which I never kept in my bullet journal before anyway)