I just collect it in a spreadsheet. There is a column for each metric, and a row for each day of the year. I try to fill it in every night before bed, but normally I'll do it once every two or three days. It only takes a couple of minutes to fill in!

Some of the columns I'll only fill in once a week. That is stuff like hours slept and steps taken, where all I do is enter the values on the health app on my phone.