1 slight knowledge of music
Let's get started! This is a lot easier if you are a girl or a guy with a particularly high singing voice, but do not be discouraged. It is rather easy to get to do this.
Step 1: Define your voice type.
I suggest this only for sopranos, tenors and altos so that you don't hurt your voice. I myself are a middle soprano, so I can do all of the ponies, with the exception of Rainbow Dash and Pinkie Pie. My voice just doesn't do that. Here are a few suggestions of voice types for ponies.
Fluttershy- Light and airy Mid Soprano
Dashie- Guy-like Alto/tenor
Rarity- Pompous High Soprano
Twilight Sparkle:Brainy Alto
Applejack- Country slur Mid to low soprano
Pinkie Pie- Energized VERY high soprano.
Pick your pony accordingly.
Step 2: Find a few starter lines.
Rainbow dash: I can do that in ten seconds flat!
Applejack: Now what the hay did you do that for?
Pinkie pie: Isn't it GREAT???
Twilight Sparkle: Dear Princess Celestia...
Rarity: Oh my stars, darling!
And there you go! Try them out and contort your voice to match the character's by adding a country slur, a british-y accent, going up about half a pitch, down half a pitch, you should know .
Step 3: And for all you crazies....
Another idea for the more sane out of all of you, you can now animate youtube films and you and your (Hopefully existant) friends can voice act them. Just follow all these simple steps, and create phenomenal pieces of pony culture. Love and tolerate, everypony!!!!