As good as it feels to purge and clean, it doesn't attack the problem: the source of the stuff. Generalizing for a bit, the nature of the stuff in question does matter, so some of my ideas may not translate across all realms of purchasable goods. However, I've found that the less I buy, the easier it is to maintain my owned items. Plus, the whole "saving money" thing.
1) Focus on the bad.
There's a Buddhist meditation technique called Patikulamanasikara that kills lust by focusing on the negative aspects of the human anatomy. While we're not engaging in the removal of lust for human beings (that seems rather unhealthy unless you devote yourself to a monk's life), it's a useful technique for everyday shopping. Make a "pros" and "cons" list, and really pour over the cons.
I'm not promoting being a cynic and being cranky about everything, but instead of visualizing the best situation, try to visualize the worst. For example, don't imagine a new gadget will renovate your life and change the way you live. Honestly, how often does that even happen? Rather, imagine that it's just like every other mediocre gadget you have. It doesn't change anything and leaves a bad taste in your mouth. You're left with buyer's remorse, and the gadget ends up in a drawer somewhere, eating up your time and space. Maybe that's not the reality, but it's closer to the truth than what we usually build up in our minds.
2) Focus on what you already have.
If the key is entertainment or leisure, it's hard to argue that we need more media when we're already surrounded by more than most people can ever consume in a lifetime. Most people have backlogs of every media format, or they have some hidden gems they forgot about that they haven't experienced in a while. The best way for me to forget about a desire or want is to go read a book. It readjusts my priorities in a positive way.
And this can encompass many other things. You probably have access to a library, which alone can busy a person for an entire lifetime. The Internet, and the legal side of Internet downloads. Your friends and family. All of these resources can keep you engaged without buying anything.
But for non-media stuff, we still forget what we have. Are you sure you can't go without? You've gone without your entire life. Just wait. Keep waiting.
3) Use and buy smart.
You likely have a computer if you're reading this blog, so you're capable of accessing more useful information than you can ever imagine. Use it to get the most out of what you have. If you need to buy something, fine, but use the Internet to figure out what will work best for you.
This does a few things. It makes your purchase more geared toward what you need, and how to perform whatever task you need the stuff to do. But it also makes the purchase slightly more arduous, and forces you to think about whether or not it's useful in the first place. You start to think like a utilitarian, focused on the end-game.
If you wait long enough, somebody probably has what you need that you can borrow, have, or buy for cheap. Yes, this requires patience. Sometimes it's not easy. But you can get your stuff for less money or even none at all.
I went without a bike for three weeks, and I walked instead. But when I got myself a relative's perfectly serviceable road bike for no cost, it was worth it. Now somebody else has less trash and I have what I need.
5) Avoid advertisements and purchasing tricks.
As previously discussed, advertisements are successful at making consumers irrational and think about purchases differently. But remember that stores are designed to get you to buy certain items. If you're shopping, have a list and stick to it. Be aware of the environment. Never impulse buy. You can always get it later.
I used to fall into the trap of "well it's on sale, so if I'm going to get it, I should get it now." If it's worth buying, you can wait and maybe miss the sale. It won't kill you, and it will give you more time to ponder the purchase.
6) Do it for you.
Don't buy stuff for anybody but yourself. This seems obvious, but too many times you'll find that what we thought was a need was actually an external standard we were projecting onto our own lives. So do it because you think it's right, not because somebody told you it was. Take advice but keep your salt shaker handy.
You don't need to buy something to be like your hero or favorite blogger. Actions define us.
7) You don't have to upgrade.
Just because there's a new Macbook Air doesn't mean you need to buy it. It's easy to think that you should upgrade because, well, it's something that I know I use a lot, I should have the best there is, right? Not necessarily. Again, these products are designed to make you want to upgrade. Be realistic about the differences between models. You're fine where you are; do you really need this new upgraded version to make things better? Likely not.
Your gear doesn't make you more minimalist. Your actions do.