Let's look at some exercises. Follow the link and enjoy doing the exercises
http://www.tolearnenglish.com/exercises/exercise-english-2/exercise-english-4253.php
http://www.english-grammar.at/online_exercises/tenses/t058-present-simple-progressive.htm
http://www.montsemorales.com/gramatica/AlltenseAfSw-2.htm
http://www.english-grammar.at/online_exercises/tenses/past-simple-progressive3.htm
http://www.myenglishpages.com/site_php_files/grammar-exercise-tenses.php#.VRajqeasW8x
http://www.englisch-hilfen.de/en/exercises/tenses/will_future_mix.htm
http://www.tolearnenglish.com/exercises/exercise-english-2/exercise-english-4253.php
http://www.english-grammar.at/online_exercises/tenses/t058-present-simple-progressive.htm
http://www.montsemorales.com/gramatica/AlltenseAfSw-2.htm
http://www.english-grammar.at/online_exercises/tenses/past-simple-progressive3.htm
http://www.myenglishpages.com/site_php_files/grammar-exercise-tenses.php#.VRajqeasW8x
http://www.englisch-hilfen.de/en/exercises/tenses/will_future_mix.htm