As with all art mediums tartan design can reach an end result which may or may
not appeal to the end viewer - there is no formula or 'correct' approach. A simple
check may be more effective than a complex stripe sequence - yet some of the
most effective tartans do have more complex sequences. A simple range of colours
may be more effective than a large diverse range but again some effective tartans
use a wide but closely co-ordinated range of colours. If you are serious about design
it is worth looking at some existing registered tartans noting ones that appeal
(and maybe those that are especially unappealing) and analysing aspects like
the choice of width of adjacent stripes, whether a pattern exists within the
sett itself, colours - close or complimentary, etc.
There are some 'tricks' or techniques that are used. Some argue that the essence of tartan design lies in recognising the combination of the mirroring of the stripe sequence combined with the horizontal and vertical replication - this resulting in a level of pattern form belying its basic components. Use of colour sequences in different widths of stripes can be used effectively. Highlighting of wide bands of dark color with narrow bands of light colour can emphasise a pattern that may otherwise be lost - this is sometimes referred to as the 'under-stripe' and the 'over-stripe'.
Although a tartan is essentially abstract i.e. the same pattern can be scaled from very small as perhaps used in a silk tie up to large as in a woollen blanket - scale still has to be taken into consideration. If, for example, the sett size is doubled a kilt would look very different from one made from the standard sett. Many registered tartans are in fact the 'same' tartan but at different scales.
Keith Lumsden, a tartan researcher of many years experience based in Scotland, has written a short guide to designing tartan