I always look at body shape since both males and females can have oviposters.
A male tends to have a slimmer more streamlined build, smaller looking eyes, a poutier thicker mouth, and longer ventrals.
A female, if you look very carefully, usually has a lighter area on her sides where her ovaries are and her body is in general more rounded (darker girls' ovaries are harder to find!). Females usually have smaller beards when flaring.
There are always exceptions of course but these are what I look for. :)