Pattern-mixing can be a little tricky, but not if you follow these three basic guidelines.
1. Mix the Patterns
You can generally group all menswear patterns into four broad categories: 1) checks/plaids 2) stripes 3) repeat prints (polka dots, paisleys, wild animals, etc) and 4) textures (like hopsack, herringbone, etc). Try pairing one with another, and avoid "stripes with stripes" or "checks with checks". When in doubt, use a solid to balance everything out.
2. Offset The Scales
Look carefully at the size of the patterns together. They should each be a different scale. One big, one medium, one small - for example. The small one should be very small. There is taste in subtlety and patterm-mixing is all about restraint.
3. Distribute the Strength
The patterns should also be different levels of “boldness” or “loudness”. One pattern should be faint and not very noticeably. One should be more conservative; evident but not overpowering. And one can be a little more bold and flashy, within reason.
Here are some examples of these basic concepts in action, from the Articles of Style archives:
The suit pattern: glenplaid, medium scale, very subtle (tonal) colors.
The shirt pattern: bengal stripe, small scale, medium strength colors.
The tie pattern: paisley, large scale, bold strong colors.
The coat pattern: solid texture (camel hair), to anchor it all down.
The suit pattern: chalkstripe, large scale, very bold.
The shirt pattern: bengal stripe, very small scale, very subtle (light blue/white).
The tie: grenadine texture, extremely tight scale, solid color.
The jacket pattern: hopsack, medium scale, very subtle.
The shirt pattern: bengal stripe, small scale, subtle (faded mint/white).
The tie pattern: plaid, large scale, higher contrast/more bold.
The suit pattern: micro houndstooth, extremely small scale, very subtle/tonal.
The shirt pattern: double-stripe, medium scale, strong/high contrast.
The tie pattern: solid texture, to tie it all together.
The suit pattern: glenplaid, medium scale, medium strength.
The shirt pattern: candy stipe, large scale, bold strength.
The tie pattern: solid texture, to to it all together.
The suit pattern: solid texture (oatmeal flannel).
The shirt pattern: block stripe, medium scale, bold strength.
The tie pattern: polka dot, small scale, medium strength.
I hope this helps give you have ideas for mixing patterns.
Just always remember - less is more.
Thanks, as always, for reading.
Yours in style,