Here's a getting started guide from the /r/transvoice discord:

Broadly the two main gendering qualities to a voice are weight and size. With voice training the general idea is to:

1. ear train: learn to recognize when you weight is heavy vs light, when size is large vs small

2. mimic and experiment: learn to produce voices that are different weights and sizes, and esp. how to balance those to produce a typical feminine voice (suitably light and small)

3. practice: just keep listening and recognizing when you're slipping up and to adjust your voice back into the feminine range, over time and lots of persistent practice, this habituates and becomes your voice!

For exploring weight:

• https://www.youtube.com/watch?v=a0PpzrWsTUE
• https://clyp.it/nwreza0c

For size:

• https://clyp.it/jdquw5ac
• https://www.youtube.com/watch?v=BW8X2nXexQs (this video has some pedagogical flaws, but is still good for listening / experimenting to some extent)

For more about the balance of weight and size:

• https://www.youtube.com/watch?v=uVJuUoypVHE
• https://clyp.it/hu53kin0

Videos to help guide expectations for beginners:

• on goals: https://www.youtube.com/watch?v=JYSxobwWypI
• on daily practice: https://www.youtube.com/watch?v=fylIX28mlyY

For beginners it can also be helpful to explore more achievable lower-pitch feminine voices:

• https://www.youtube.com/watch?v=5OyfNLWf3UM

To ear train, it's commonly recommended to listen to and "play along" with Selene's clips:

• https://selenearchive.github.io/

Note: as you experiment or do any voice training exercise, make sure to pay close attention to:

• how it sounds to you as you do it,
• how it sounds when you record it and play it back for yourself,
• how others report they hear it, and also
• how it feels (in your body) when you produce the different sounds, keeping mental note so you can reproduce the voice if you need.

Experiments to try:

• using a pitch detector, sing a note and chant a word while maintain the same pitch, and change resonance/size from dark/large to bright/small while keeping pitch the same
• using a pitch detector, keep pitch steady and practice going from a heavy to a light weight without changing pitch
• mimic a large voice, like Patrick from Spongebob, or the Giant from Jack in the Beanstalk
• mimic a small voice, like when you talk to a baby or a cute puppy or animal, or accessible overfull childish voices, like Ash Ketchum from Pokemon or Dexter from Dexter's Lab
• mimic a heavy voice
• mimic a light voice
• try producing an underfull voice intentionally
• try producing an overfull voice intentionally
• try going from full masc to overfull
• from full masc to underfull
• from full masc to full fem
• from full fem back to full masc
• from underfull to full fem
• from overfull to full fem