You can do it however you want to, from staying away from the grocery store to not buying anything except necessities, like toilet paper and coffee. Some people do it for a full year while some go on a fiscal fast for a week or a month.
Even if you do it for one day now and then, you will save money.
The key is to not spend anything at all unless it's absolutely necessary for a certain period of time.
Don't think you can? Think again. Instead of having a pizza delivered, cook something you already have. Instead of new clothing for a special event, wear something you already have in a different way. Instead of buying a magazine off the rack, go online and read or read a book you already have.
It's not a matter of "can you do it," it's a matter of "will you do it." If you're serious about saving money, you'll do it.