Wait for sales & specials. This is why I love Forever 21. If you browse through the Daily Specials and Fabulous Finds, you can find so many awesome items at great prices! I also wait to order from Drugstore.com because they periodically send out free shipping offers with a $25 purchase. Also check out sites like Hautelook, Ideeli, BeautyTicket, and BeautyStory for discounted sales!
Sign up for email subscriptions. Alrighty, maybe many of you actually don't like getting bombarded with promotional emails every day, but let me tell you, those annoying emails can come in very handy sometimes. If you want to keep up with the latest sales, steals & deals, promo codes, and more... I think it's a good idea to subscribe to your favorite companies to get their updates. You might get some notifications that you might miss otherwise! Ulta, ELF, Cherry Culture, and MAC (to name a few) usually send out a lot of good promos!
Use promo codes as much as possible! I make it a habit to check Retail Me Not before every purchase I make from any online store, because chances are, there's probably a promo code floating around the net that I can make use of! I've always been able to find a good ELF promo code to use from Retail Me Not!
Don't buy only because of hype! Do YOUR research before taking the plunge into a newly raved about (and possibly expensive) product. Sometimes, it might not be all that it's chalked up to be. You wouldn't want to spend your money just to end up disappointed! If you're unsure of a product, read as many reviews as possible or see if you can test the product in-store before deciding to buy.
Try not to buy things you know you don't need. I must admit, I used to be the person that would buy literally ANY beauty product that caught my eye, "just because." But after I started piling up stuff I didn't use, I realized that this wasn't a smart shopping strategy. I was wasting my money AND storage space, all for the hype of a product or because I felt like I might need it later (which I knew I really wouldn't) when I already had many similar products. Try not to buy more products if you know you have something similar at home, or don't buy it unless you REALLY have your eye on it.
Try not to make spur-of-the-moment purchases. Resisting the urge to randomly just throw stuff in your cart on a routine trip to Walmart WILL save you a lot of money. Trust me. Now I know we're all beauty addicts and our habit is quite expensive... but you don't always have to end up buying a new lipstick or mascara every time you go grocery shopping (this was one of my biggest bad habits before).
Make a wishlist or to-buy list. I found that creating and maintaining a wishlist gave me more incentive to only buy items on my list, just so I could cross them off (yes, this gives me a weird feeling of accomplishment for some reason :P). This also helps me to avoid making those dreaded spontaneous "just because" purchases.
It's okay to splurge every once in awhile. We all know how expensive MAC, YSL, Chanel, Dior, etc. can be. However, I think it's a good thing to make a little bank-breaker purchase ONCE IN AWHILE. Again, do your research to find out if the product is really worth the price tag. For example, I would NEVER have thought that I'd spend anywhere near $30 on a lip gloss, but I eventually took the plunge and bought a $30 YSL Gloss Pur and it was worth it. Sometimes, it's nice to spoil yourself!
Set a budget for yourself. Do whatever works! If you wanna spend $20 a month on beauty products, go for it! If you wanna spend $200, go for it! As long as you can set a budget and stick to it, it should help. But of course, asking your significant other for a little money, honey... doesn't hurt either ;)
Try a spending ban every now and then. If all else fails and you STILL feel like your beauty spending habits are taking over your life, then maybe your best bet is to try a beauty no-buy for a certain amount of time, or try a Project 10 pan (or something similar), where you can only buy yourself a new beauty product after you've finished or "hit pan" on a set amount of beauty products you already own.