To check the fit of your shoes, try them on at home on a clean surface — carpet is ideal, so you don't scuff or damage the soles. Give yourself a little space to walk as normally as possible.
A good fit should feel secure but not tight, with a little room at the toe. Remember that leather softens and moulds to your foot as it's worn in.
Keeping your shoes in unworn condition — no marks inside, on the uppers or on the soles — means you can still return or exchange them if the fit isn't right.