What are the steps to be undertaken while writing a .install file for drupal 7 module? I want to add an table to the database using .install file of a module. I am creating a completely new module which has not been enabled till now.
Which are the functions required in the .install file

function [HOOK]_install() {
  switch ($GLOBALS['db_type']) {
    case 'mysql':
    case 'mysqli':
//Should I write my query to create table inside this ...
    case 'pgsql':

   break;
}
}


function [HOOK]_uninstall() {
//Should I write the code here to remove the table after installation


}
as Clive says you should use hook_schema for creating your custom tables and then 
hook_update_N
https://api.drupal.org/api/drupal/modules!system!system.api.php/function/hook_update_N/7
for the updates of your tables module.