Just go to your ssh client and run

chown -R someuser:somegroup public_html/

Making it accessible to drupal you would probably run

chown -R www-data:www-data files/

Migrating drupal site from one server to other could be easy and fast task, then again if not prepared you could run into many problems and have lots of work.

There are many tutorials how to setup memcache, but many are also old and have things you don't really need.

You can find here updated tutorial for that
http://www.howtoforge.com/installing-memcached-and-the-php5-memcache-mo…

You can manipulate your users and databases with SSH access, but then again its nicer and easier on the brain to make it trough visual interface (for most, some will probably work it faster in prompt). But for that you still need to install phpmyadmin through lines of SSH access.

When importing data you will probably be extracting or unpacking a tarball File
To unpack or extract a tar file, type:

tar -xvf file.tar

To save disk space and bandwidth files are saved using compression program such as gzip or bzip2. To extract / unpack a .tar.gz (gzip) file, enter (note -z option):

If you need to archive your files and you want to exclude some folders, for example "files" folder or some subfolders of files. You can use gzip for it

tar --exclude=sites/default/files/* --exclude=cache/* -cf file.tar . && gzip file.tar

And you will have a nice zip archive without folders you maybe don't want to transfer.

If you have some stackscript, like you might have on VPS like Linode, where you have automaticly installed some linux distribution like Debian, and then Apacher, PHP and MySQL are also installed, this will not work out of the box, you will still need to add some extra stuff on your VPS so you could install some drupal sites.

Sometimes your drupal DB will have problems, and it will cause slow queries, especially when having many nodes. Log to you phpMyAdmin and select all tables in DB and click optimize or repair, this could fix many problems and make your site run smooth again.