How to sync my Dropbox files with a preferred local folder?

Dropbox currently does not support syncing folders outside the Dropbox folder, according to their web site.

However you can achieve this by creating a symbolic link between the Dropbox folder and the other folder you want sync, using this command:

sudo ln -s ~/Dropbox  **/path/to/another/folder**

So when you go inside /path/to/another/folder, you will be taken into ~/Dropbox
Make sure the other folder is accessible after linking.

According to their site https://www.dropbox.com/help/12/en you can't sync folders outside the Dropbox folder, but there is a workaround in Ubuntu

To get other folders synced into Dropbox you have to create a symbolic link from the target folder to the Dropbox folder

For example:

ln -sfn ~/Documents ~/Dropbox