When one is doing a still life and there are various
things in it, most of us work to get the shapes and
proportions right. But that is not where it should
end.
After getting all that down in the best way you can,
take care to focus in on the details and really confront
what is there. I have seen many students just sort of
toss on a suggestion a bottle top.
So really confront the contours of it - the perspective
of the cylindrical opening and what part of the back
ring comes around into the curves in the front.
And if the bottle top is below your eye level, as in
this photograph, really get the curves right so it looks
three-dimensional!