netselect-apt automatically creates a sources.list file for using with apt for the specified distribution by downloading the list of Debian mirrors using wget and choosing the fastest servers (both US and non-US) using netselect. The output file is written to OUTFILE.
If there is an INFILE (by default "mirrors_full") which lists the Debian mirrors, netselect-apt uses that rather than downloading another copy. The file will be downloaded from http://www.debian.org/mirror/mirrors_full
Install netselect-apt in debian
Open the terminal and run the following command
#apt-get install netselect-apt
You can start using the following command
wait while the different mirrors are tested. When it’s finished, you will end up with a sources.list in the directory where you executed the command in.
Move it to your /etc/apt/directory by executing the following command
mv sources.list /etc/apt/sources.list
and then update the source list
Now, you would have the closest Debian mirror setup which would give the best download speeds.