The Width of the lapel and the position of the notch are the most prominent indicators of the year the suit was bought, so ensure that these 2 details are not aggressively slim or positioned too high up.
There should be no folds of cloth (too big), nor ripples (too small), the space here should not exceed the width of an average fist.
Base of your sleeve:
½” of your shirt’s cuff has to be visible.
Top of pants:
Pants should sit on the hips, not hang over them.
Pant legs should fit close to your own leg but not be tight nor voluminous. Also, avoid aggressive tapering.
The seam on the shoulder of the suit should line up exactly with the end of your shoulders, this is the measurement that should dictate the size jacket you rent/buy, it is also the only are you should never have altered.
The body of your jacket should fit close to your torso. It should not create a “boxy” look.
Bottom of the Jacket:
Historically a tailor would have you drop your arms to your sides, cup your hands and check that the bottom of the jacket sat right in that “cup”. Jackets are being cut shorter these days and should fall somewhere right below your derriere.
Bottom of the pants:
Slim cut trousers are worn shorter – approximately ¼” below the top below back of the shoe; more generally the back part of the pant leg should end between the middle of the heel counter and the beginning of the shoes sole. Basically have little or no break.
With the top button closed, the jacket should fit close to the body but should not strain.
It is always undone.