Sometimes, it is emotional. A relaxed person might talk really slow as they rest on the couch. Someone really tense might talk quickly as he or she prepares for opening night at a play. There are many reasons you can invent. Try inventing some and choosing a pace that fits.
Accents can be fun to use.
Just ask a friend who speaks with an accent different from your own. It can be fun to try and mimic each other's accent. Try finding an example of someone using an accent. Listen to it carefully and begin to pick up how the person pronounces words. Accents also have a rhythm.