You spent your 20s building an inventory of the basics , and now it's time to step up your game. Your 30s will bring many milestones, and between all the personal and professional events — promotions, weddings, black-tie parties, etc. — you'd better have the necessary outfits.
That means a formal dress, tailored pants, and a sexy blouse that isn't quite as revealing as the one you wore on your 25th birthday. Consider this your wardrobe checklist and start scrolling to shop the essentials.
Source: IMAXTREE 
The Real Leather Jacket
If the denim jacket was the go-to layer in your 20s, in your 30s, it's a leather one, like this Club Monaco leather jacket  ($695). The effect is cool without being too edgy or tough, so you can absolutely slip it over your polished dresses and top your trousers with it, too.
The Cashmere Sweater
Replace the stack of tired knits in your closet with a supersoft cashmere sweater, like this one from J.Crew Collection  ($188). Unlike your pilled and faded cotton pullovers, this one will look smart with a pencil skirt at the office or dinner.
The Polished Trench
Sure, you can still get by with your anorak on a rainy day, but there's something inherently classic about a trench coat like this Gap style  ($128). It will look just as sharp with your weekend denim as it will with your work sheath.
The Top That Shows Off Your Best Assets
In your 20s, you had a collection of "going-out" tops that were flirty and fun; now it's time to upgrade for a sexy, sophisticated top that showcases your best assets. If it's your shoulders you want to draw attention to, try a halter like this Tibi Silk Top  ($198) that's subtle and polished, but undeniably sexy. Whatever your best features are, this is the time to flaunt them with the right top that puts the right parts on display.
The Perfect Pencil Skirt
You're stepping up your game at the office and at home, and a pencil skirt like this one from Tory Burch  ($295) does the same. It adds just enough interest to elevate a white blouse, but it's still totally classic, so you'll have it for seasons to come.
The Grown-Up Coat
Long gone are the days you could wear your puffer or anorak with your sophisticated pencil skirts and get away with it. A lean, go-with-everything coat in a beautiful hue, like this Diane Von Furstenberg Michaelee belted wool coat  ($795), is the perfect piece to finish off your cold-weather looks with ample polish and so much more sophistication than your anorak.
The Printed Trouser
You've already made the switch to clean, skinny-fit denim; now you need a casual pant that can go from work to weekend in a flash. Printed pants, like Ann Taylor's windowpane slim ankle pants  ($89), maintain that same lean, simple silhouette, but they're a bit more dressed up, should the weekend call for a more pulled-together look at brunch or dinner with parents/friends.
The White Blazer
With a classic schoolboy blazer already in your closet, up your game with a steamlined white blazer  ($104). The effect is elegant and a bit more grown-up — plus, a white blazer is totally seasonless, so feel free to add it to everything from your holiday attire to your Spring dresses.
The Made-to-Flatter Sheath
In your 30s, you've graduated from jeans and t-shirts to more pulled-together fashion moments. So, you need a dress you can pull out and look amazing in at a moment's notice. For everything from spontaneous date night to a big meeting, you need a dress that flatters your frame, makes a statement, and most importantly, one that you feel completely confident in. We'd look for something with special details or a standout print, like this Rachel Roy leopard print sheath  ($139).
You made your post-collegiate upgrade with skinny black pants, and now it's time for another step up with a pair of tailored trousers, like these Bop Basics Work Trousers  ($180). The key is finding the most flattering silhouette for your body — a long lean leg-line flatters practically everyone, but you may want a slimmer fit or a wider leg depending on your figure. And, by all means, get thee to a tailor if necessary.
The Black-Tie Dress
The wedding  circuit that started in your 20s shows no signs of slowing now, only friends in their 30s are throwing even fancier affairs. For this reason and so many more — like that random black-tie gala for your significant other's work — you need a formal dress, like this BCBG Max Azria Kailo draped one-shoulder gown  ($298), in your arsenal. Like actually in your closet — not one you're borrowing from your big sis.