What all should i do for my baby (3 week old) yellow belly mud slider turtle?

I have it in an aquarium with a light and i feed it food pellets and it has a coral thing where it sleeps and sunbathes. I also hav lots of pebbles piled up for it to get out of the water. I catch minnows too and put them in. I want to make it as happy as POSSIBLE. How should i play with it, and make it happy and all kinds of stuff. Please help cuz i want it to be VERY happy. Thanks :)