It all depends on how your money is committed, for eg over 1/2 of my income is alloated to my morgage, followed by a PL/ Credit cards and a monthly payment on my PC.
So first thing you need to look at is where does your money go? What do you have to pay, these are usually not negotiable, if you have a morgage and have been paying extra look at seeing what you bank can do if you only have the one income. Options like extending from 25 yrs to 30 reduces repayemnts because they have you on the hook longer.
Secondly things like cable TV, newspapers and magazine subscriptions can go. These are the luxury items that you dont want to live without but can.
Thirdly consider what you are eating, I dont know about you but every fortnight when I go shopping I feel like my bill is being hiked up yet again.. You may have to substitute items like Toilet paper, paper towels, for less expensive brands.
Consider what you eat and where you can compromise for eg steak goes except for special occassions mince and sausages substitute or better still meatless meals, when my 4 where little we had one income we were big meat eaters but I soon learned that protein came from a variety of sources so some meals contained meat others didnt.
I would also advise buying baby items like bottles, nappy liners, etc when you shop one or two things a shop. You need to consdier that you may intend to breastfeed but for a varity of reason be unable to, you may plan on using disposable nappies and again be unable to....contingency plans are very important...stock up on non perishable items where possible.
When you are on one income consider shopping online if its available in your area, I actually do this to send gifts to my mother of grocery items and have noticed that I dont overspend because Im not in the shop buying "added extras".
If you are in your own place consider what you can grow yourself, vegies and fruits trees (although the trees will take a few years to fruit) and maybe chickens if your local council allows it.
The best advice I can give is to buy a freezer and cook double and freeze, this does same in energy and time. You can also buy seasonal items and freeze you will need a good freezer cookbook but I survived many a time on what was in my freezer when an unexpected bill popped up...yes I know a good budget resolves that issue but I was good at budgeting until recent years
so you are now getting hindsight advice.
I guess what Im saying is write everything down, clear what you can before the second income goes, stock up where you can, my daughter did with all sorts of things so she had essentials while she wasnt working and most lasted until she had to return to work.... and remember if you get into difficulty with bills approach the lender ASAP to resolve the situation, never ignore something important as you are morel likely to get assistance if you appear to want to reslove the issue.
Best wishes.