There is no specific way of getting characters, but if you take really good care and don't feed him when he is not hungry, you should end up with Mamemitchi or Mimitchi (depending on whch generation you are on) and bad care will end you up with Maskitchi or Gozuritchi, again depending on which generation you are on.
yah... its says to keep training between 3-7 and only feed it once when its hungry and stuff like that... i actually wanna try to see if that will work, but i will have to wait till next gen.