Well, you're not a person who can't save money. But leave that aside for now. For the moment let's think about the problem this way: there are two people wearing your body and living your life and making your decisions. One of them wants to save money and one of them doesn't.
Tip #1: Treat both of these people as fully rational and intelligent. Because they are. There are lots of excellent reasons for spending money. There are good reasons (though fewer) for spending money you don't have. Your spendy self is not a willful unteachable brat. She's a human being with deep and important reasons for doing everything she does. Find out what they are. Find out why she thinks these things are more important than saving money. Honor her intentions. She's not going anywhere. Your solution is going to involve either enlisting her, or tricking her. Enlist her if you possibly can, because it's not as easy to trick her as you might think.
Tip #2: Trick your spendy self if you can. If you have an employer with a savings plan, which lets you save your money before you ever see it, and makes it hard to take the money back out once it's in, then do that.
Tip #3: If you're self-employed, or in debt, that won't work. You're going to have to enlist your spendy self. Get her on your side. Find the moments when she spends too much, and interrogate her about them. Why does this expenditure seem so imperative? What's at stake? Don't treat her like a naughty child. Treat her like an adult. She might be right, after all. But it's likely that you can persuade her that whatever end she's trying to achieve by spending this money -- generally, making somebody happy -- can actually be better served by NOT spending it. Saving that money rather than buying a treat -- that is the treat. You're buying them, and not just yourself, financial room to maneuver. You're buying freedom. You're buying treats to enjoy later.
Tip #4: Realize that they're out to get you. I don't ordinarily encourage this frame of mind, but in this case it's totally appropriate. They are out to get you. The marketers and credit card companies and banks, the media, often even your friends, are all trying to manipulate you into spending money. If you feel like the target of a plot, its because you are. Cultivate paranoia and even a little hatred. This economy is, by design and with full intent, a machine to manipulate you into spending so hard that you have to work ever harder just to keep up, so that you never have time to pause, never have time to think it over, never have room in your life for art or God or love or contemplation. Push back. They'll nickle-and-dime you into submission, if they possibly can. Screw them. That's not what life is for.
Tip #5: Remember, when you're scrimping: you are already this poor. You are not pretending to be poor in order to be rich later. You really are this poor, and by saving twenty percent of what you make -- the bare minimum, for most people, to set up a comfortable retirement -- you are simply facing the facts of your poverty. Face them boldly and fiercely. Be proud of being a person who understands reality and is willing to be real. Do it for yourself, and do it for the people you love. They need your example.