I forgot to mention a couple of my favorite tricks, which work nicely with a microphone. If you drop your volume and lean into the microphone then it will sound as if you are right next to the listener, whispering in their ear. This can have a wonderful effect to distinguish between “asides” and dialogue. It can also create a real intimacy with your listener.
Listen as I demonstrate.
Another handy trick is left-right balance. This isn’t a reading thing, but a post-production effect that can do a lot to create the idea of different speakers even with only one voice. When you record something with multiple characters, read the whole thing straight through, for pacing doing all of the character voices.
Then go back and read each piece of dialogue individually. Do all of a character’s dialogue in one go, then go back and do the next character. Besides giving you a more consistant vocal quality for the characters, you can separate them into left and right channels. Most people choose to leave the narrator in the middle. It does a lot to distinguish between characters. But it will add a lot of work to post production.
If you have time, do multiple reads so you can select the best take for each line.
If you listen to my Rampion I read the narrative three times and each of the character dialogue breakdowns twice. The characters are separated into different channels–this does mean that the file will be larger to download. For downloads I could have saved a lot of space by keeping it mono.