Formal to me is a tuxedo and up. Suits are semi-formal since they’re worn during both day and night. A properly fitted vest and tie is another option.
Dress shirts – Dress shirts are tailored shirt typically with a structured collar. The underside of the collar has a pocket for collar stays (the little plastic things many men throw away and never put back in). The stays keep the collar from warping and present a polished appearance. Plastic stays warp and were only intended for store displays. Splurge and buy the metals stays for a dollar. You’ll be happy you did.
Dress shirts also have a straight hem at the bottom and are longer because they’re intended to be tucked in. NEver wear a dress shirt untucked and try not to wear them with jeans. You’ll look confused.
I was once told that a nice suit is to a woman what sexy lingerie is to a man. I’ve found that to be remarkably true.
The key is that it needs to fit properly. Assuming a two button suit, the top button should button at or near the natural waist to accentuate a masculine V-shaped torso. The back should be wrinkle and dimple-free when standing straight up (tailors can remove the dimples you find especially the ones at the back of the neck). Flat front pants are typically the best options .and should be cut trim with the waist between your hips and natural waist depending upon your level of comfort. For now don’t cuff your pants unless your tailor explains to you in detail why you should do it with this suit and not another.
Vests – vests are the hardest to get right because they need to fit flush to the body without wrinkling. They also need to be long enough to just cover the belt loops on your pants. Men today who wear vests that come so high in the back that you can see their shirt are trying but it just looks like it shrank. That being said a properly fitted vest (or waistcoat) can present a very masculine powerful image especially when worn with a tie and dress shirt with the sleeves rolled up.
Shoes- oxfords preferably. Keep the broguing to a minimum. Shoes with a lot of broguing (the holes punched in the shoes. . think a wing tip) make them far too casual for most suits.
Ties – don’t cheap out on the ties and never buy those boxed shirts and ties. They look ridiculous. I suggest Drakes of London for ties and pocket squares If drakes is out of your price range, you’re in luck. The resale price of a tie is absurdly low. Go on ebay and get them for pennies on the dollar.
Pocket squares – I prefer large-scale patterns especially if I’m not wearing a tie. In fact a pocket square can replace a tie in most casual suit situations.
Socks – if unsure match your socks to your pants and NEVER your shoes. Once you’re comfortable with that match the color to something above the waist, like a color in your shirt, tie, or pocket square.
A final note on suits. A good suit feels like a second skin and is totally comfortable to wear. It exudes confidence, success, value, and self-respect. A bad suit is ill-fitting, uncomfortable, and tells the world you’re either wearing this against your will or you’re not successful enough to know how a suit should look. With this in mind a bad suit is a waste of money and places such as Jos A Banks, men’s wearhouse, and other such discount suit shops are to be avoided. If you’re on a budget you still have many good options including SuitSupply and EHaberdasher.com