Most men learn to tie a particular tie knot as a child and then stick with the same knot throughout their life. This can lead to their ties looking a little odd when worn with particular shirt collars. Learning to tie a few different tie knots and understanding which collars to match them with will quickly improve how you look in a bespoke office suit and tie.
The basic principle behind choosing a tie knot is that you should be filling the space left by your shirt collar; wide cut collars should have thick knots, while straight cut collars should have thin ones. If you combine a thin knot with a wide collar then you'll end up accentuating the width of your collar, which will look strange. Similarly, a thick knot will not fit properly within a straight collar.
As your choice of tie knot should be determined by your choice of shirt collar, the first choice you should make is which style of collar would best suit your face and neck. In general, men with large faces and thick necks should opt for a wide cut collar, whereas those with narrower faces and necks should choose a straight collar. Matching your collar and knot to your face will ensure that the lines of your shirt and tie and those of your features balance out. In this way, your collar and tie won't cause your face to look unusually large or small and vice versa.
The most common knot to match with a classic straight cut collar is the four-in-hand. This is a simple knot that doesn't use much of the tie's length. As such, it is a good choice for tall men who want to wear a regular sized tie. For people who want to experiment with a wide cut spread collar, the double Windsor is the most common knot to choose. This knot uses a lot more of the tie than the four-in-hand and, as a result, taller men may need to buy extra long ties in order to have a tie of the correct length. The half-Windsor knot is between these two in terms of thickness and is a good choice for classic or button down collars.