Mastering Blockchain Programming with Solidity

Always add new variables at the end

You should always add a new state variable at the end of all the existing state variables:

//Good Practicecontract SampleContract {    uint256 public x;    string public y;    uint8 decimals;  // New variable added}

In the preceding code, we have added a new state variable, decimals, at the end of the existing variables declaration.