Some breastfeeding mothers can tell which side they are on without an external reminder. I am not one of those mothers. I know the importance of switching sides, and starting each nursing session on the other side (keeps milk production balanced). So I need a little help.
I use a thick band ring (like this or this) I have that I switch from side to side. When I nurse, I choose the side with the ring on my hand. When I start nursing, I switch the ring to the other side.
Other moms have other methods of keeping track of where to begin. You can clip a safety pin to your bra, or these pretty mama jewels. You could also use any bracelet, or the ones made for this purpose. There are a number of rubber bracelets on the market for this. They come with sliders on them for marking the time and you switch them from wrist to wrist. The trouble is they are rubber, and, for me, I don't want things on my wrist, especially for a number of months/ years, and especially a thick rubber bracelet. I love my ring on my hand from side to side. On my left hand, my index finger is the same size as my right hand ring finger.
I also use the Itsbeen Baby Timer to help me track baby. I use the baby timer to count up, although it also has a feature where you can set it to flash or buzz an alarm after a set amount of time has passed. I find it incredibly useful to know how much time has passed since baby started nursing, or fell asleep/ woke up, peed, or pooped. It is set with buttons for sleeping, feeding, diaper, and wildcard. When I pumped the first few weeks, I used the wildcard "*" button to time the length of the pumping sessions. It was great for that purpose as well, because the lights were always visible. There are smart phone apps that have baby timers, but the screen goes dark after a few minutes. With Itsbeen, you can always see the time moving. Another feature I like is the little light that goes on but lights it up in blue. This is nice at night because it isn't too bright. It also has a clock, although sometimes, and especially at the beginning, how long it has been since something happened is far more important than where you are on the 24-hour clock of a day.