The solution is to iterate down the list looking for the correct place to insert the new node. That could be the end of the list, or a point just before a node which is larger than the new node.
Note that we assume the memory for the new node has already been allocated and a pointer to that memory is being passed to this function.
// Special case code for the head end
void linkedListInsertSorted(struct node** headReference, struct node* newNode)
// Special case for the head end
if (*headReference == NULL || (*headReference)->data >= newNode->data)
newNode->next = *headReference;
*headReference = newNode;
// Locate the node before which the insertion is to happen!
struct node* current = *headReference;
while (current->next!=NULL && current->next->data < newNode->data)
current = current->next;
newNode->next = current->next;
current->next = newNode;