There are so many options, and so much source
material for 1940's fashion. Dresses, suits, skirts, knitwear, hats
and coats and gloves, all easily obtained, either genuine vintage
gear if it'll fit you, or reproduction.
Shoes - beware, some genuine vintage shoes can
be fragile, so treat them with respect, and don't wear them in the
rain as the glue can be brittle. There are some very good reproduction
shoes available, but as always, do your research to make sure your
footwear is appropriate.
Hair should be well groomed, make up should be
subtle, apart from well defined lips, in many shades but more commonly
Victory Red - ladies were encouraged in the UK to be glamourous for
the sake of 'our troops'.
There are many uniform options too, if that is
what you want to portray - Land Army, WVS, WAAF, factory worker, housewife,
etc - just make sure you do your research and get the details right.