The width of your tie needs to match the width of your lapels.
It’s pretty basic but so many people go wrong either because a) they don’t know this or b) they just don’t have another tie to wear with the suit.
If you are among the “a” people then now you know, no excuses! If you are the “b” people then either go buy some more wide/skinny ties or don’t wear a tie with your suit. As tempting as it may be, a skinny tie looks awful on a wide lapeled suit and vice versa.
For those of you reading this confused.. I’ll go into a bit more detail. The lapels are the part on each side of a coat or jacket immediately below the collar that is folded back on either side of the front opening. Some jackets have really wide lapels, others really thin. Usually a skinny fit suit will have really thin lapels which is why they look great with skinny fit ties obviously.
If you have a ridiculously wide lapeled suit like the one shown below, then obviously don’t try to find a tie with the same width.