When I'm alone at home, I sometimes read comics, manga, or video game text aloud. It usually boils down to several main voice types.
Normal (not that deep): Usually used for youngish to teenage characters, like Luffy, Edward Elric, Matsuda, Usopp etc. Pitch varies depending on the character (Usopp is higher than Luffy).
Sort of Deep: Used for 'badass' or serious older characters. Zoro, Blues.exe, Zero, etc.
'Smooth': In between Normal and Sort of Deep, with a trace of accent. Used for characters like Sanji, Jean Havoc, Aiber, etc.
Deep: Used for the big, tough dudes. Smoker, Crocodile, Alex Louis Armstrong, Sloth, etc.
Jackass: Normal with a 'tude. Sometimes add some nasal.
Authoritative: Usually used for adult males. People like Soichiro Yagami, Yuuichiro Hikari, Cerveau, King Bradley.
Old: Ranges from senile sounding to something vaguely reminiscent of Chikao Otsuka. If I make it weedy enough, it can double for old women as well.
Female: This is like, one voice, with differing softness/hardness depending on the character. I can't do them very well, cuz I'm a guy.
Reading stuff outloud is fun because I can practice acting. Since I sing in my school's choir, it's relatively easy for me.