As a singing teacher with a particular interest in transgender vocal techniques, these are the main points I've found:
1) Don't obsess or overcompensate over pitch.
The pitch difference between male and female voices is not as great as people think it is (closer to around a fourth than the octave usually assumed) and is certainly not consistent across all men and women. I've worked with women with naturally low voices and men with naturally high ones.
So start working with what you've got, pitch-wise. Increased range will come with practice and physical realignment, but trying to imitate Barry White from the get-go would be like me going to the gym and trying to imitate Arnold Schwarzenegger.
I'll give an exercise at the end of this to help with range, but for now focus on:
2) Resonance.
Any sound or voice is a mixture of different frequencies affected by the size of the thing vibrating (in this case, your vocal folds), the area in which it does so (your larynx), any connected sound boxes (your chest) and filters through which the sound is passed (your throat, glottal, nasal port, lips, teeth etc). By understanding this, with practice you can emphasise the deeper frequencies you covet. This will mostly involve learning to open out the larynx and avoiding constriction, which you'll find hard unless you first work on:
3) Deep breathing.
If you've studied Yoga, Pilates or any similar discipline you'll have learnt to use abdominal and/or lateral muscles to control the diaphragm to make full use of the air in the lungs ('shallow' breathing from the chest is inefficient, does not provide sufficient airflow over the vocal folds and leads to constriction as you try to cause vibrations with neck muscles instead). I don't think I'm allowed to link to my articles on this yet, so for now I'll just point you towards the nearest Pilates class to get you breathing the right way. This done, get used to dropping the tension from your neck into the floor so your larynx can open out and resonate.
This still won't make you convincing though if you get caught up in;
4) Stereotypes, gender myths and other bunk.
Did you know that all women speak in frilly sing song voices, never swear, choose sentences as if they've stepped out of a Jane Austen novel and cry at the slightest provocation? And that men all have gruff, monotonous caveman voices that sound the same whether they're ordering a romantic meal or commentating at a monster truck rally? No, me neither.
In the real world, people are people. There are differences between the sexes but they're not always the ones people think of and nothing cries phony like someone obviously trying to modify their personality and behaviour to an exaggerated stereotype that just isn't them. Since the whole point of this is to be yourself as you really are, beware of anyone who tells you you need to pitch everything like the voice over for an action movie trailer (or the Voice of The Mysterons) and reduce your conversation to the level of Beavis and Butthead. While social conditioning does affect the physical vocal conditioning, even that is variable between cultures and geographical locations and there are a lot of red herrings.
Now, because you've been good and attentive and read this far, let's get back to pitch.
5) Siren Song.
This exercise, known as sirening for reasons that will become apparent, is possibly the single most useful vocal exercise there is. With it you can explore and expand the full range of your voice, smooth out gear changes between chest, head and falsetto registers, experiment with changes in resonance and work on specific pitches.
First, say the word "Sing", but instead of finishing off the 'g' consonant hold on to the sound between the 'n' and the 'g', "ng". You should find yourself humming a tone with your mouth slightly open and your tongue flattened out across your mouth lightly touching your upper teeth. Now begin to raise and lower the pitch of that sound so you sound like an old fashioned police siren (hence the name).
As you move the sound up and down, be aware of the physical sensation of how the sound vibrates around your body and anywhere there is unnecessary tension (typically in the neck - see above). Every day when you practice, work on sliding down to the bottom of your range and immediately bouncing back up again, like a rubber ball. As you do this you are training your entire vocal tract to get used to operating in that range, strengthening the muscles and, over time, expanding your range to incorporate deeper sounds.
There are still physical limits - deep soul notes will be as unrealistic for you as virtuoso soprano notes are for me (mezzo soprano I can do), but you won't get near those limits (or even know what they are) unless you work at it.
Hope this is useful, it's an area I'm particularly interested in professionally so would be grateful for any feedback.
