Accessories for a suit

Pocket square:  a pocket square should be of equal width and length as the name suggests. 
​The most versatile silk squares measure between 16″ and 18″ in width. This may seem large for something that occupies a small breast pocket, but it’s important for the pocket square to have some volume, as this allows it to stay up on its own and not fall into your pocket.
Meanwhile, a cotton handkerchief may be smaller at between 9″ to 12″ in width. As cotton is often folded and ironed to the right size, it doesn’t quite need to be as large as a silk pocket square.
Pocket squares are generally made from silk, cotton, and linen.
Ties: The classic necktie is one of the most popular and professional forms of neckwear. Indeed, this simple garment adds a level of formality to your attire and either make or break and entire outfit.
The rule of thumb dictates that tie width should roughly sync with the width of your lapel. Your ties’ widths should also sync with your body type, first and foremost. Acceptable tie widths range anywhere from 2.75″ on the narrow end of the spectrum and 3.5″ on the wide end.
With all of that being said, it is essential to know that the length of a tie should always sit at the same spot regardless of the man wearing the tie. Your tie should be tied to match your torso length and waistband. When standing in natural posture, the tip of the tie should end in the middle of the waistband/belt.
Tie-clips: A tie clip, also known as a tie bar, is a menswear accessory that’s used to keep a necktie in place by attaching it to the shirt with which it’s being worn.
A functional form of jewelry, tie clips are available in a massive array of colors, materials, styles, and price points.
 It’s so important to understand how to use a tie clip and the basic rules of wearing one.
  1. Place the tie clip around the shirt opening
  2. Slide the tie into the gap and release the clasp
  3. Check your work
  4. Admire your tamed tie
Correct tie bar placement: The tie clip typically sits between the third and fourth button down on your dress shirt.
A waistcoat or vest precludes the need for a tie bar, as the waistcoat is performing the same function the tie bar would. Wearing a tie clip in a case like this would be sartorially redundant, which robs it of all its style points:

Bow-ties: The bow tie is a controversial item. Beloved by dandies, college professors, and the sartorially adventurous. Generally not appropriate for most business settings, the bow tie is the rare menswear item that has a cult following alongside a cult loathing.
Any bow tie, regardless of its style, should be approximately the same width as your face when knotted. If a bow tie is too large, your head will look smaller. Conversely, if the bow tie is too small, your head will look enlarged.
Bow ties are not for every guy, or for every situation. Their festive nature makes them an excellent choice for grooms and for very formal evens then.
Cufflinks: Cufflinks are menswear accessories that hold shirt cuffs together. A form of jewellery, cufflinks are dressy. They’re thus worn with single and French cuff shirts, which are dressier than barrel cuff shirts. 
Cufflinks are made from different materials like: carbon fiber, crystal, glass, gold, silver, titanium,… 
Dress shirts with French cuff styles require cufflinks
How to put on cufflinks:
  1. Put on your shirt and fold one cuff back over itself. If you’re right-handed, we suggest starting with the left cuff.
  2. Insert the cufflink closure through the two outside cuff panels, making sure that the cufflink’s face is visible on the outside of the cuff.
  3. Push the closure through the two inside panels. Be sure that the inside panels are flat and flush against the outside ones; do not curve it underneath the outside panels as if you were buttoning a barrel cuff shirt.
  4. Fasten your cufflink.
  5. Repeat steps 1-4 on the other cuff.
Color matching:
  1. If your links are metal (nickel/silver, gold/brass, etc.), it’s best to ensure that your metal matches any other metals in your ensemble: belt buckle or suspender adjusters, the bit on your shoes, and jewelry. Note that this isn’t a hard-and-fast rule, but rather a strong guideline.
  2. If your links are a color or combination of colors, pick another item in your outfit with which to coordinate them. The guidelines here are quite loose, as cufflinks don’t share a visual plane with much of anything. Coordinate their color with that of your shirt, tie, pocket square, or even your socks.
Pins: A lapel pin is a decorative trinket of some kind that men wear on the lapel of a suit jacket, sport coat, or blazer. 
Lapel pins have seen a resurgence in popularity in the last 15 years or so. They are a way to show membership in social clubs, professional organizations, or to simply add visual interest to a tailored ensemble.
Correct lapel pin placement:
  1. Lapel pins always go on the left lapel
  2. The pin is the reason for the lapel’s buttonhole. Put your lapel pin in your buttonhole. This is much easier if that hole is functional, and any tailor can make this happen for you in a matter of seconds. However, you can easily pierce the hole if the pin is sharp.
  3. As an exception to rule number two, place your pin just inside the buttonhole if you’re already wearing a lapel flower in your buttonhole 
  4. Some lapels will have a small loop of fabric on their underside just beneath the buttonhole. This loop’s purpose is to hold the stem of a long-stem lapel pin in place so that you don’t have to poke it through the lapel itself.
Lapel pin with pocket square: While there are no rules regarding pocket squares and lapel pins, it’s always smart to have them be colour coordinated to some degree
Different type of pins: Long pin, floral pins/flowers, badges & custom pins