I have a weird system for tracking my injections. I found an "injection map" image online: basically, a picture of an abdomen with the shaded part representing where you can inject. I divided that into 12 areas: six on the left, six on the right, where each side has two rows of three. My map therefore looks like this (center part is a two-inch gap around the navel):

1 2 3 ------ 3 2 1
4 5 6 ------ 6 5 4

I use a notebook where the page is numbered 1 to 30, to represent 30 days. I printed out the abdomen image, with my six zones marked, and taped it inside the front cover for reference.

Day 1, I inject left side, zone 1, and I write L1 in the notebook.

Day 2, I inject right side zone 1, and write R1 in the notebook.

Day 3, left side zone 2, L2 in the notebook.

... and so on. After I reach R6, I go back to the beginning and repeat.

I know this seems OCD, but honestly, it's a breeze to open my notebook and see what's next.

When my pen finishes, I rip out the page, create a new page numbered 1-30, and just make a note of the last injection zone.