Rent is the big one. Buy a house instead so that the money will at least become equity. Or find a way to live rent free, such as agreeing to housesit, or living with someone who needs someone in the house at night (old folks with big houses sometimes offer free rent for this). Or do what I am about to do, move into a small camper van or motorhome.
Cook your own food and freeze or can it so they you can have convenience food without getting take out food or buying expensive processed food. I can my own food and it is not nearly as hard as most people think. It's healthier, too and home canned food makes great gifts.
Get the kind of credit card that you have to load with money ahead of time. Only use this credit card. That way, you cannot get into trouble owing any money but will have the convenience of using a credit card.
Get into the mind set of learning to do more for yourself; I am learning to cut my own hair. Change your own car's oil, decorate your own jeans, bake your own bread, cater your own parties. Do as much as you can for yourself. If you can't do something, see if you can barter with someone who can. Go to the website Freecycle to see what you can give away or get for free. You'd be surprised what they have.
Sort out your clutter, things stored and see what you can give away, what you can sell. You might discover some extra money by selling stuff you don't need.
Spray your license plate with cooking oil or, if possible, the commercial stuff used to keep your license from being photographed by one of those red light cameras; those tickets are very expensive. You can look it up online but if you can't afford the sprays they sell, cooking oil will work amost as well.
Ask your accounting department at your job to automatically deduct as much as you think you can put aside each month. That way you will not have to think about it at all. If you don't make it a huge sum, you may not even notice its absence from your check.
Read: How To Make $1,000,000 In The Stock Market Automatically by Robert Lichello. If you follow this guy's instructions, invest a fairly small amount of money, and use his easy system, you will be a millionaire in about 10 years. Investment companies use his system all the time. This system works whether the market is good or not because it doesn't depend on stocks going up, only on volitility which we have plenty of right now.
Question every expense and ask yourself if you can do without it or find a much cheaper way of dealing with it. That is the basis of a lot of savings.
the cheaper grocery stores is a great idea for the basic foodstuffs. I recently had to furnish my own apartment from scratch, and shopping at thrift stores saved me a bundle.
Probably lots of things -- cook at home instead of eating out, rent movies instead of going to theaters, use coupons and go to sales at stores instead of just buying whatever you want, etc.
four days we eat healthy and on a friday we eat fish fingers and chips or burgers and chips. on a saturday and sunday him and his kids eat at his parents. shower instead of taking a bath. buy in bulk. write a shopping list and stick to it. dont buy snacks, because it costs money.
Usually the small things make the biggest difference, like:
Stoping eating out.
Take your own lunch to work with you.
Walk to as many places as you can to save money on petrol or bus fares.
Only buy yourself clothes if you REALLY need them.
Cut back on vices, like drinking, smoking or anything else. (it will improve your health too).
Set yourself a weekly budget, and stick to it!
Shop at cheaper grocery stores.
Technically you could cut back on everything.
If I have no idea how you live though, so answering this is kind of hard if you want something specific.
Cook at home instead of eating out and pack your meals for work. Shop sales and use coupons; if a store offers you their free discount "card," sign up for it. Check retailmenot.com for coupons on all kind of merchants. If you have a cell phone consider cancelling your landline, and cancel any utilities you don't really use or need... like premium cable or anything like that. And don't do any impulse shopping... before you buy ask yourself if you really need it right now or not. Good luck :)
Keep track of what you spend, and it might become easier to see where you could cut back. I like the web site mint.com. It's free, and you can use it to track all of your finances (similar to Quicken, and I think it is actually owned by them.)
Coupons can also save you a lot of money. There was a great blog series a while back by a man who was able to feed himself for $1 a day for a full month. It's a real eye-opener: http://www.grocerycouponguide.com/articles/eating-well-on-1-a-day/
I agree with TheHypocrite.
But one thing I've found to cost a lot of money is eating out at restaurants/fast food places.