nginx provides packages for Debian in their own repository, allowing you to install the most recent version rather than the older versions provided through the main repositories.

Add these lines to /etc/apt/sources.list:

deb http://nginx.org/packages/mainline/debian/ jessie nginx
deb-src http://nginx.org/packages/mainline/debian/ jessie nginx

Change jessie to wheezy if you are still on Debian 7 "Wheezy".

Download and add nginx's public key:

wget http://nginx.org/packages/keys/nginx_signing.key && cat nginx_signing.key | apt-key add -

Update the package list and then install nginx:

apt-get update
apt-get install nginx

By default, the latest version of nginx will be installed, but if necessary, you can also specify a specific version to install.