The most important factor is colour, and we have already established that navy blue pairs well with many other shades. Broadly speaking, colours can be divided into warm, earthy tones and cooler, greyscale shades. Colours such as navy blue, brown, beige, moss green, and various tones of these harmonise well with each other. Blazers in these shades often pair well with trousers in another of the previously mentioned colours.
The cooler palette consists of shades of grey, black, and white. Blue, brown, and green also often complement a lighter shade of grey.
Choosing an odd blazer and odd trousers in the same colour but slightly different tones can work well, for example, a dark blue blazer with dark blue jeans. Often, the look appears more balanced when the blazer is slightly darker than the trousers rather than the other way around. Similarly, a darker grey blazer pairs well with lighter grey trousers.
A beige blazer with beige chinos in a different fabrics is rarely a good combination, it does not resemble a suit. Another myth worth dispelling is that "black blazers go with everything." Not quite. Black creates a very stark contrast with most other colours. Additionally, there are nearly as many shades of black as there are black garments, so avoid trying to match black trousers with a black blazer unless they are part of the same suit. However, black and washed denim jeans work well with most black wool blazers because the texture contrast is sufficiently noticeable.
Blue jeans in light to mid-blue or white pairs well with a vast range of blazer colours and patterns.