You should come up with your ideal maternity leave situation. Then, review it through a "reality check" lens and figure out which points you are willing to do without in order to get things that you really need. I wanted to stay home as long as I could, so instead of taking three months of maternity leave, I asked my employer for two full months and two part-time months of leave. He gladly accepted, because I would at least be back in the office within two months.
Once you have a plan, make an appointment to discuss it with the appropriate individual at your place of employment. Do not leave it for the last minute! The outcome of putting off the conversation because you don’t want to negotiate has one loser -- you! Give yourself some time to negotiate.
Last but definitely not least, no matter what agreement you reach, maternity leave is still leave! If your employer starts calling you every day to get you to do things from home or come in one day a week, PUT YOUR FOOT DOWN! This is your time and it will be over before you know it. Kindly remind them that you just had a baby and that you are in no condition to do anything but take care of yourself and your child.
I have a friend who was getting paid maternity leave. By the second week they had already asked her to come in to work for a day. By week four, she received a call letting her know that "a month was enough" and that they wanted her back at work. She refused and offered them to stop paying her while she was out.
She made two enormous mistakes: First, she went in to the office during her week of maternity leave. She was pregnant for nine months; they had enough time to prepare for her absence. She is not the owner or principal of the company. And, second, she willfully gave up her paid maternity leave! She should have refused to go back, period! If they wanted to stop paying her then they would have said something, but she put that offer on the table, so guess what happened? They stopped paying her.
So remember, do your research, make a plan and negotiate. But most importantly, STAND YOUR GROUND!