Basically there are a few things that you need in order to really start being able to get your voice into a feminine range:
1. Pitch control. This is one of the things that makes a lot of trans women have a hard time working on their voice at all, is that they really don't have the vocal control to maintain certain pitches, and therefore don't have the control to keep their voice in a certain female range. To work on this, do some non-trans-related voice training. Work on building up strength. Work on being able to hold musical notes. Do some scales, slides, vocal warmups, hums on certain pitches, and just work on being able to maintain certain pitches without your voice warbling and sliding back up or down. You'll need this control in order to be able to really work on pushing your voice higher. (Side note: if you went to a voice-training coach, this would probably be what you'd spend a majority of your time doing. Their #1 goal is teaching vocal control. So it would basically be pitch exercises and phrasing exercises.)
2. Work on pushing your range higher. Once you have the pitch control in order to do it, now you can actually work on using the female range, which will slowly train your voice to speak there. You can do this by speaking and singing at the very top of your chest voice, and in your falsetto voice. (I tend to find singing easier, because it's more fun, and feels a bit less ridiculous to me.) Try to copy the pitch of female singers and the pitch of female speakers. Sing/speak right along with them, and try to copy their speech/singing as best as you can. The basic point is to work on making sounds in that vocal range consistently, which will slowly "train" your natural voice to speak in that range. You can also do this, as Calpernia Addams and Andrea James suggested in their voice course, by using the musical note A, 220 Hz, which is 2 notes below middle-C on a piano. Play that note, and then try to speak using that pitch. Start out with simple "Haaaaa...."s, then move on to a simple phrase like "this is the voice I want to use," and then move on to speaking entire sentences just using that note. (Yes, it will sound monotonous... but the point here isn't to sound realistic yet, just to train the vocal muscles to use that range consistently.)
3. Work on your resonance. You can do this by gargling, (yes, that is the method that a lot suggest... that "guh" sound that you have to make in order to do it actually does push your larynx higher,) or by doing techniques deliberately designed to push that larynx higher. Swallowing is a motion that does that. So try to feel which muscles you are using when you do that swallowing motion which pushes the larynx higher. The way that I did this was actually by trying to replicate the singing tone of folk singer Joan Baez, which required pushing the voice higher and forward into the head. That's the basic thing that you are trying to do here... push the voice away from your chest. Feel the vibrations of your voice. Where are they coming from? Move them higher. Push it up into your neck, then up into your head, and then forward, until your voice is coming from the very top of your throat and resonating in your head rather than your chest. Men tend to speak from the bottom of the throat, letting the voice resonate in the chest. Women tend to speak from the very top of the throat, resonating their voices in their heads.
4. Work on pitch variation/dynamics/expression. Basically, women speak in a very "free" dynamic manner with a lot of pitch variation, a lot of expression, and as a whole it feels very emotionally "free" rather than monotone and restrained. They use pitch to accentuate words rather than volume and staccato like guys do. This step is where, after you've got the pitch and the resonance, you really make it sound female. The only way that I've really found to do this well is to just study how women naturally speak, and trying to copy their phrasing and pitch. And again, repetition, repetition, repetition. Do it over and over and over and over again, until it starts to become natural. There are many subtle little things that women do in terms of inflection and pacing and pitch that you're really not going to get any other way except to be around actual women and study how they speak. Many have suggested finding an actress that you like how she speaks, and then repeat back every single line that she says, trying your absolutely best to replicate her tone of voice and pitch and inflections EXACTLY. Include all of the pitch dynamics, all of the little upward inflections and slides, and again, just do it over and over and over again until it starts to become natural.
And most importantly, remember, this takes TIME. Lots and lots of time. Months. Probably even a year or more before it will really start becoming natural. I started voice training over a year ago, and I still feel pretty inadequate compared to cis-women. The important thing, though, is to just remember that it takes time. You're basically doing the vocal equivalent of learning to play a new instrument. And anyone who's learned an instrument can tell you, you don't learn how to play overnight. You have to keep working at it, practicing and practicing and practicing, until your hands finally start to get the muscle memory to do it. And it takes years of this before you can really become good.
So practice consistently, don't get frustrated and give up, and just keep working on it, day after day, week after week, month after month, and slowly you will see improvement. You just have to learn to keep practicing even when you feel like you're not getting any better.
