Length
As far as I can find, a wand's length has nothing to do with magical ability. The only correlation between the wand and the wizard here is possibly height or personality:
All wands have their individual lengths and may also be some correlation between a person's size and the lengths of their wands. Rubeus Hagrid, who is half-giant, owned one of the longest known wand; it was sixteen inches long and made of oak.
According to Garrick Ollivander, matching a wand to a wizard solely by height is a crude measure. Long wands tend to suit those with big personalities, of a more spacious and dramatic style of magic.
— Wandlore, Harry Potter Wikia
'Neatness'
I've found one reference to a correlation between wand 'neatness' (whatever that is, in a wand) and how refined one's magic is:
Neater wands favour elegant and refined spell-casting.
— Wandlore, Harry Potter Wikia
Woods
There is some more indication that the type of wood a wand is made from has some correlation with the wizard's calibre:
[Acacia] "A very unusual wand wood, which I have found creates tricky wands that often refuse to produce magic for any but their owner, and also withhold their best effects from all but those most gifted."
From Ollivander's notes on wand woods — Wand Woods, Pottermore Wikia
The proper owner of the aspen wand is often an accomplished duellist, or destined to be so, for the aspen wand is one of those particularly suited to martial magic.
— ditto
No doubt there's more; I'll keep researching and updating this answer as I go.