1. Honor thy tailor

Even the best suits need altering. Pants need to be shortened, jackets need to be brought in, sleeves need to be narrowed (yes, you can ask your tailor to slim down your sleeves), and buttons need to be realigned with buttonholes (most guys’ shoulders aren’t entirely even, meaning your jacket often sits a bit askew). You should always buy your correct size, but you then need to have a tailor customize it to your body. It’s the difference between being appropriately dressed and being stylishly dressed

2. Thou shalt wear sneakers made for a man

It’s fine to own crosstrainers and running shoes and hightops. But save them for the gym. When you’re on the street, keep your sneakers simple and classic. Go for ones like Stan Smiths, Jack Purcells, and Sambas. They work with everything, including suits.

3. Thou shalt invest in the right timepiece

Buy a high-quality stainless-steel watch. It looks as right with jeans as it does with your best blazer.

Hit the jump for the rest of the rules.

4. Thou shalt match your socks with your suit

When choosing socks, the basic rule is to consider the suit instead of the shoe—in other words, if you’re wearing a navy suit with black shoes, reach for navy socks. And when wearing a light suit, make sure the socks are darker than the suit but a shade or so lighter than the shoes.

5. Thou shalt not wear a tie that is too slim

Unless you’re a hard-core fashion guy who favors a superskinny tie, stick with one that measures about three inches at its widest point. It will be narrower than traditional ties, but not by too much. Tie one on and you’ll look modern and sophisticated.

6. Thou shalt put your wallet on a diet

Your wallet should not be as fat as a burrito. In fact, you should get rid of your wallet and, while you’re at it, trash all the receipts, video cards, and other unnecessary crap that’s stuffed in it. Buy an elegant, slim leather credit card holder and stock it with your essential cards. Then, fold your cash in a money clip. All that other nonsense can go in your desk drawer. You don’t need it.

7. Thou shalt wear the right tie with the right tux

Two points to remember: (1) A bow tie goes best with a peak-lapel tuxedo, while a straight tie works better with a notch lapel. (2) Regardless of what kind of tie you’re wearing, make sure the fabric matches the lapel. If your lapel is grosgrain, your tie should be grosgrain. If your lapel is satin, your tie should be satin. And one more thing: Your tie (no matter its shape) should be black. Colored ties are for the prom.

8. Thou shalt wear brown shoes—with nearly everything

Black dress shoes are easy—they’re understated and tasteful. Brown dress shoes up the style factor. People notice them. They go best with gray, khaki, or navy. Dark brown shoes are easier to pull off than light brown ones.

9. Thou shalt learn when to cuff ‘em

If you’re wearing a trim, modern suit with flat-front pants—the kind often shown in this magazine—you should not cuff your pants. However, if you’re a guy who likes a classic suit with a single pleat, go for a cuff—but not more than one and a half inches deep.

10. Remember thy undershirt

This one’s tricky. If you’re wearing a conventional white broadcloth dress shirt (which means it’s fairly see-through), you have two options: Skip the undershirt and you’ll look clean and stylish. Or, if you’re a hairy guy who perspires a lot and you feel safer in an undershirt, wear a crewneck. The lines of a V-neck or tank top will be visible beneath your shirt and tie and you’ll look cheesy. If you prefer a V-neck or tank top, you might consider other dress shirts. Go for ones with checks or stripes, which make an undershirt less visible. Or opt for hardier fabrics, like an oxford cloth, which make undershirts all but invisible.