The sleeves of the suit must be long enough bedecking your wrist. Your shirt length should be more than that of your suit jacket.
Stitching threads should not show on your suit.
Always try your suit before buying to see if there is a free movement or not.
As far as slits are concerned, the best option for thinner men is no slit and for the bulky ones, the better option is two slits.
As important is the jacket in suit fitting, equally vital is pant. For correct waist size, ensure that there should be at least a space of two fingers.
Pleated trousers have always been in fashion but the latest fashion is of flat-front pants. Cuffed trousers are just perfect for taller men. But for shorter ones, it's a no.