We are complex beings and our behaviour frequently lands us in complicated situations, something you should try and reflect in your fiction writing. Things are rarely cut and dried in the real world, so it is a good idea to tie some intriguingly complicated knots in the story you are working on. Your heroine may love somebody but not be in love with them; she may be frightened of the consequences of being successful in either her professional or her personal life; your hero may be attractive yet unsympathetic all in the same breath. It is within these areas of ambivalence that tension grows and tension is an extremely handy tool to have in your writing armoury.
Things are rarely black and white — it is in that ambiguous,blurred area that most of us live and where interesting fiction is often kindled. Although you should always be aiming for clarity in your writing: the well-realised character, the taut plot, not to mention crisp, new-minted prose, try not to exclude a little bit of healthy ambivalence at the same time. Instead, go for grey and see where it takes you — my hunch is that you will arrive in an interesting space full of creative uncertainty.