<apex:commandButton onclick="saveAndnewmethod()" value="Save and New"/>
<apex:commandButton onclick="savemethod()" value="Save"/>

function save(){
  //...common lines
  if(someValidations == true){
  $('.savebtn').prop('disabled', true);
  save_ACC_Cont();//this is an action function of button save
  }
}
function saveAndnewmethod(){
//...common lines
  if(someValidations == true){
    save_and_new();////this is an action function of button save and new
    $('.savebtn').prop('disabled', true);
  }
}