Happily, at the moment it's still early on in the Debian release cycle, so not too many packages are missing from, or outdated in, stable. However, it can be really useful to grab packages from upstream when needed without necessarily upgrading your whole system to testing. This is quite straightforward to do with apt, but it isn't all that well-documented.
First, add the testing sources to /etc/apt/sources.list:
deb http://ftp.us.debian.org/debian testing main non-free contrib
Run apt-get update. If you get an error message like this:
E: Dynamic MMap ran out of roomedit /etc/apt/apt.conf to contain this line:
APT::Cache-Limit "10000000";and rerun the update.
Now edit /etc/apt/preferences to include these lines:
Package: * Pin: release a=stable Pin-Priority: 700 Package: * Pin: release a=testing Pin-Priority: 650apt-get prefers options with higher pin values, so this prioritizes stable over testing.
To install a single package from testing, use apt-get install packagename/testing. However, this doesn't grab any dependencies, so you may not be able to run the upgrade. The alternative is to use apt-get install -t testing packagename, which will try to meet the dependencies if possible.
Note, however, that sometimes it's not. For example, if the upgrade will break other packages, you may just have to make do without it!