Using a thesaurus

To improve your vocabulary, it's a good idea to use a thesaurus (sinónimos).
There is an excellent free one here:-
http://www.macmillandictionary.com/about_thesaurus.html

Here's how it works using 'sad' as the example.
use the dictionary
http://www.macmillandictionary.com/dictionary/british/sad
read the descriptions of sad, choose the meaning you are interested in and click on the red 'T' below the entry.
'feeling unhappy, especially because something bad has happened'
http://www.macmillandictionary.com/thesaurus/british/sad/sad_4/Feeling-sad-or-unhappy
'making you feel unhappy'
http://www.macmillandictionary.com/thesaurus/british/sad/sad_11/Making-you-feel-sad-or-upset