Ideally, when to wean is a decision that you and your baby make together. Realistically, as many moms head back to work, this may be hard to do.
If you have been told to wean because of a medication you are taking or because of an illness, pregnancy, or surgery, make sure you ask me first. There's a bunch of bad information out there and lots of unnecessary weaning taking place. And if you are weaning because you've been told that breastmilk has no benefits after a certain time, just keep nursing. No formula has come close to breastmilk, despite what they advertise, and there is no cow out there making better milk for your child than you are.
Weaning is almost always accompanied by some guilt and regret. I hope all of you know that I am really impressed with all the work that you put into nursing. I have helped some of you through very difficult starts to breastfeeding and I'm continually amazed at the motivation that you have to continue to breastfeed through very difficult circumstances. Please realize that 50% of the women in the USA don't even try to nurse. Your kids are very lucky to have moms like you.
Kids who are ready to wean are distractible, spend less time during feedings and may be more interested in solid foods. If we let the baby lead in weaning, we wait until they decide they want to nurse, without initiating or refusing to nurse. That way, the baby can cut back on the amount of feedings.
More likely, it's mom who wants, or needs, to wean. There are many ways to do this. The most common involves cutting back on one feeding every 3 days or so. The feeding should be replaced with lots of cuddling and close contact and if the baby reacts poorly (they may do things to get more attention) then we should slow down the process. And it's nice to try to replace the "work" feedings first, meaning, eliminate the feedings where you will be working or away from the baby first, and leave the nighttime and first morning feedings for last. In fact, you can keep those feedings for months after you eliminate the other ones.
If your breasts get uncomfortable, then pump just enough to relieve the pain. Weaning too quickly can lead to mastitis and plugged ducts. You can use ice packs, tylenol, ibuprofen, and cabbage leaves, just as we did during the early days of engorgement. Never do any breast binding-- that still shows up as as a way to stop milk production in some older references. It can lead to all sorts of bad things!
We should wean the baby to formula if they are under one year of age, and to cow's milk if they are over a year. I don't care which formula or which kind of milk. They can be weaned right to a cup if they are over 6 months or so.
There are a few things for mom to be aware of. You may need to cut back on the calories you consume now in order to avoid gaining weight. Your breast may be a little, well, saggy for a few months (but, they were going to get that way anyway!) and you may have milk secretion for several months after you are finished weaning. Your period should start coming back, if it hasn't already, and it may be a bit irregular for awhile.