It depends how detailed you want to get. For me, I am sort of anal , and keep a record of almost every detail, even from cartridge to cartridge. Then I will keep a written summary of case prep, seating, etc So I can go back and retrace if needed.
I find that using a computer spreadsheet (such as Excel) is real good. I keep a workbook within the file for each batch. I then have a summary sheet that is simply a row showing only the critical data (bullet, case, charge, primer, velocity) , etc , so I can easily trace what powder I've used, what bullet, what primer, etc
I know thats more than most people do but it helps a great deal since I reload only in small batches and not too often.