When they're doing something while transforming, instead of just standing there gawking at their body. Especially when the activity is related to the woman they become, e.g. becoming a maid while tidying up, or becoming a tomboy while running a track. I like when it's implied the activity is causing the transformation, and they can theoretically stop it, but feel a compulsion to continue until it's too late.
When they don't notice the transformation at first, subconsciously doing uncharacteristically feminine things without realizing—like walking naturally in the heels they didn't notice their shoes had just morphed into. I also enjoy a more extreme version, where their memories are dynamically altered as they transform, thus when they do notice their body is different, their shifting memories cause them to quickly disregard it as normal.
When a guy talks about his dream girl, his features transforming to match his descriptions, until he has become his own dream girl.
During identity death, when their old name gradually changes into their new one, one or two letters at a time.
When they interact with multiple people over the course of a slow transformation, and people begin treating them differently when they start looking more like a girl.
When another girl teaches them basic things about living as a female, and helps them dress up.
When their predicament is overwhelming to the point where they burst into tears, only to be comforted by someone else. Crying girls are endearing.
Turning into a robot girl whose primary function ISN'T sexual.
When their bra/top has a lot of empty space, to be filled by their expanding breasts.
Constant reminders of how her new tits feel. Their weight, their swaying and bouncing, the way her shirt rubs against them.