Sometimes, your mac is filled up with files and you can't seem to
understand what really is taking much space. Here is how you can find out.

First of all find disk usage and save it to a log file. Also, find all
big files that are there. Grepping using 'G' would find all files that are in
GB.

Also, save the second list to another file so that we are only doing it once.

du -h > ~/space.log
cat ~/space.log | awk '{print $1}' | grep 'G' >  ~/highspace.log

Next, open a split window and do

cat ~/highspace.log

And Now, start finding the ones which are big one by one.

Let's say one of the entry was 5.6G, Let's find which one was it.

 cat ~/space.log | fgrep -f highspace.log

 #It will give something like this:

1.2G    ./.android/avd/Nexus_6_API_21.avd
2.7G    ./.android/avd
2.7G    ./.android

Now, if you feel the file is not needed and you want to delete it. Do the
following:

sudo rm -rf Documents/Movie.avi

Voila! Repeat this process and remove all files and directories that you no
longer need.

Disclaimer:

Do it very patiently and backup everything that's important. This guide is for
very advanced users and you should only do it if you know what you are doing.
I am not responsible for any data loss. Do it at your own risk.