My trick is to track every single expense.
Something about keeping track of every dime that goes out really works to reign in those expenses. I freely admit, it's a pain - mostly because I do it manually, on a simple spreadsheet. But I couldn't justify spending the money for a program that would pull data from our bank and credit card accounts to do the tracking for me.
When you start tracking, it's helpful to also create a budget or spending plan. It doesn't haven't to be elaborate - I do a quick calculation of our fixed monthly expenses and subtract that from our monthly income. The amount that's left is our discretionary spending money, and it's the outflow of that money that I track.
The goal is simply to keep the total spent that month to as far under the total discretionary amount as possible. For example, if our discretionary spending for the month is $2,500, I'd like to see the amount we spend be less than that.
I don't think of this as a strict budget. Some months we go way over the amount I've allotted for our discretionary spending and have to dip into savings. If we get close to the end of the month and a purchase will put us over, but it's something I think I really want or need, I'll make the purchase anyway. But the fact that I know we're close to our limit does make me question how much we want or need something, and that's probably the key to why this works to get (and keep) our finances on track.
Let us know if you try this and if it works for you!