There are two ways of training you're Tamagotchi.
1. If it's calling you for no reason, you should either give it a Time-Out or Praise.(in the some Tamagotchis, Tamagotchis with low training levels tend to give mean gifts to other TMGCs, if it's snickering after it gives the gift, give it a Time-Out)
2. Sometimes, if you find your TMGC ready to use the bathroom, select the toilet icon to put the TMGC on the toilet. The training level sometimes goes up when that happens.