For clothing?
On a figure, in a typical pose for the figure wearing the clothing.
A wireframe. I wanna see the wireframe.

And as already mentioned? As simple as possible.
No need for a gazillion polygons doing nothing in 3D.
Every polygon has to have "its task" in 3D.

Textures? Stick to the standard dimentions.
And choose; Bump, displacement or normal map, but do not start a mix and run chapter using them all for "something".

And last but not least: It has to be special. Something no body else can build.
Most of us have Blender or similar, most of us can build what we need.

And what do you ask? ?
Look around for similar objects and what they cost.
Be competitive or you"ll sell none. LOL.

When I see what can be bought for a dollar or 2? WHAW.
Even some freestuff items are of spectacular quality lately.

And first of all :
Build  free stuff first. Build a reputation before you start to sell.
No reputation usually means ; "No sales" either.

Poser 1, 2, 3, 4, 5, 7, P8 and PPro2010, P9 and PP2012, P10 and PP2014 Game Dev
"Do not drive faster then your angel can fly"!