(Note: this article is about Drupal, but the same philosophy applies to other content-management systems that have multisite capability, such as PmWiki's WikiFarms feature. In order to use multisites, you will need to have a hosting account that allows you to keep more than one domain or subdomain in the same account, so that they can access the same files. Generally speaking, PHP cannot run files that are in another account.)
The Drupal project has fond hopes of one day producing the most user-friendly content-management system in the world, and it's making great strides in that direction. However, it's still written by and mostly for programmers, so often the easiest way to install and upgrade it is from the UNIX command line! Many people prefer to use drush, but here's how I do it without drush. These instructions are for Drupal 7.
Alas, a good hosting company is hard to find. All too often, we find that the proverbial grass is greener in another pasture, and it's time to move. But a modern Web site is a dynamic thing, being edited by lots of people. How do you make sure that the most recent version gets copied? Here are the steps I've developed: