I used a voice therapist, best money/time in my transition I have spent.
It's hard to describe but a guy's voice, you feel it low and more in your chest, my female voice I feel it much higher, like when you hum and feel it more in your head than your chest. It is -not- falsetto. She had me repeat "Nim Nim *say another word*" as part of the practice. Also my adams apple is now normally higher than it used to be, to the point it's really not visible. This voice training moved it up as part of the practice (swallow then try to keep it in this "up" position as you speak). She also had me sing sliding scales to work my pitch naturally higher (push it every day) and to "warm up" along with other warmup I do in the shower in the morning to protect my voice. I bought a small voice recorder and a "pitch tuner" thing to give myself a starting place for practice and practice, practice, practice. We spent a lot of time on annunciation and inflection. smoothing out t's and phrases like "Ah-ha", a guy has a sharp start to the second H, a female it is very smooth and just sorta glides in. I bet I said that phrase hundreds of times before it stuck. I would do the repetitions in the car or other places I was alone. There also is a little more breathyness and you have to learn to breath from your diaphram to pull that part off. Many guys are chest breathers. One thing that helped me too was to try to mimic women on TV, repeating what they just said.
Before voice training, my "fake" female voice was just a soft/higher pitch version of my male voice and it turned very male quickly if I had to speak loudly. And usually, it might have been sorta passable for a sentence or two but I couldn't keep it up very long. Now I can speak for 20-30 minutes in front of a large group loudly and still sound female (I've listened to recordings) so the soft voice approach has limited uses.
Anyway, I now have a very female voice, haven't been misgendered from my voice now in years and it's just my natural voice. Sorta like my walk/mannerisms are now, after a while it just becomes how you are without thinking about it. It takes time and patience. Also as others said, start off slow and short periods. It took 6+ months to get where this felt comfortable to do for any extended period of time. The other thing, I was living full time by then so there was no use for a guy voice. I think switching back and forth would be very hard. I haven't used my guy voice in years now ๐