There's a couple different ways to deploy a symfony2 application. Take a look at this entry in the Symfony Cookbook: How to deploy a Symfony2 application.
After the code is copied to the server basic post-deployment steps may include:
- Configure your app/config/parameters.yml file
- Update your vendors
- Clear your Symfony cache
- Dump your Assetic assets
- Other things!
There may be lots of other things that you need to do, depending on your setup:
- Running any database migrations
- Clearing your APC cache
- Running assets:install (taken care of already in composer.phar install)
- Add/edit CRON jobs
- Pushing assets to a CDN
Personally, I usually use Capifony. I have it copy the application to the server with the third-party libaries. It then performs the post-deployment tasks I need it to do: clearing the cache, dump web assets, and execute database migrations