What to Look For in a Well Tailored Suit

What should you look for in a well-tailored suit?
While a great suit will make you feel (and look) sharp, world-wise, and sophisticated, a bad one will make you look like a hack or some man-child who still gets dressed by his mother. So, it helps to know a thing or two about buying, wearing, and caring for the one you love.
What Suits You?
Let's start with the basics. Buying a new suit doesn't start with the tailor; it starts in your head. Is the suit for work, date night or friend’s wedding? All three? Is this your first and only suit or your thirteenth suit, intended for a special occasion? Know that and you can make the right choices, starting with colour. Your best bet is to opt for one in a solid true navy blue or charcoal gray. Both colours work with every shirt-and-tie combination you can think of and a lot more (denim shirts, T-shirts, fine gauge knits). They're the standard.
There's also black, not for daytime wear and not as foolproof as you think. You imagine The Strokes, but you might end up with the security guard. If you decide to go for black, make everything as fitted as possible. You won’t look like a maître d' if the cut of the suit is as aggressive as possible.
If you want to go bolder than solid colors, your best option is going the plaid suit route. Wearing a plaid or check suit is going to get you noticed and remembered—that’s the point. Make sure you stay out of overkill territory by keeping yours to one of the trusty menswear neutrals we just talked about (that would be navy, grey and black).
Single-breasted jackets are 100% approved and always will be. Most of the suits in your arsenal should be single-breasted. But if you’re the kind of daredevil who wants to give 110 percent, step up to a double-breasted jacket. The new double-breasted suit is slim and trim, without the shoulder pads and droopy fits that signaled ’80s Wall Street excess. We like it because it projects an air of power and confidence.
There's also the three-piece suit. You can still blow the doors off the conference room in a killer three-piece. The point we must make here is that the three-piece suit is not a costume. It should not be worn with a pocket watch or a newsboy cap. (Yes, Cillian Murphy in Peaky Blinders looks suave...for 1919.)
More Details, More Decisions
Before you start getting obsessed about the size and fit of your suit, you should decide what style of suit you want. And that’s all about the construction. Two buttons or three? (Answer: almost always two.) Notch or peak lapel? (Depends on the image you’re trying to project.) Meanwhile, a fourth button (don’t do it!) or cartoon lining (eek!) can send all the wrong signals. The details make the suit.
If you go the single-breasted suit route, your next course of action is to figure out the button stance that's best for you. All or most of your suits should be two-buttoned. This is the modern standard. One-button suits are good for formal, nighttime events and for skinny rocker types who can wear anything (damn them). Unless you are an advanced suit-buyer, don’t go for a three-button suit unless the third button is hidden behind a “roll” of the lapel—an Italian move—so it looks like a two-button suit.
Next, we're moving on to lapels. There are two types most common in everyday suits: peak (because they flow up and out toward your shoulder, ending in a point) and notch (self-explanatory). Going with a notch lapel is like ordering the roast chicken: it's a total fail-safe. A peak lapel is flashier and more formal, a brasher, power move compared to the standard notch.
Don't ignore the back of the jacket. It plays an integral role in a suit's character. Most suits have rakish double vents these days, but the single vent is still a classic and perfect for a smart-casual look. No vent however, = no dice. No vent is like having no friends at school, if you opt for it, you’ll find yourself similarly deserted.
You also need to consider your suit's pockets. The most common example are flap pockets, featuring a rectangular flap of fabric that hangs about two inches over the front of the pocket. Patch pockets look like they were originally found on sporting jackets and are stitched to the outside of the jacket, not the inside. The sartorial net effect is that they give off a more casual, utilitarian vibe. Besom pockets are found on more formal jackets and tuxedos and have no flap. They're super-clean and mean but not right for the office.
No matter how much it costs, a suit is only as good as its tailoring. Fit is everything. Once you’ve decided you want a two-button, single-breasted suit with a notch lapel, a double vent, and flap pockets (nice work - it sounds like a winner), you’re ready to focus all your attention here. It doesn’t matter if your suit costs 50 or 10,000; if the thing fits like a sack of potatoes, it’s not good. 
Suit jackets are shorter than they were a decade ago, but you don’t want your entire derrière showing, either. If you hang your arms loose at your sides, your fingers should be able to easily cup the bottom hem of your suit jacket. Any shorter and you’ll look like a doll. Longer and you’ll look like an undertaker.
Your Shoulders: A tailor can't fix a saggy shoulder, so make sure the seam ends right at the outside of yours. You want military precision here.
Your Chest: With the jacket buttoned, the lapels should lie flat on your chest. If they bow out, you need some alterations. The modern way is to keep the lapels moderately narrow. For the record, the rule of thumb on lapel size goes like this: Big, wide lapels are for alpha men, skinny lapels are for slick rock-’n’-rollers. The rest of us should fall somewhere in between.
Around Your Torso: With the jacket buttoned, slide your thumb between the button and your gut. If your thumb is snug, good. If it's a little loose, you’ll need to have your tailor take the jacket in a bit in the back.
Your Arms: The sleeves should hug your actual arms, closely following your natural lines, and stop in time to show half an inch of shirt cuff. Most people don’t consider the width of their suit sleeves, but it’s imperative to do so.
Your Pants: Fasten your pants at your natural waist (about an inch below your navel). Too loose? You know what to do: Talk to your tailor. One more oft misunderstood/neglected step: If there’s too much fabric through the leg (i.e., if you can grab a fistful), ask your tailor to taper them. It’ll create a cleaner, slimmer more contemporary line.