These are useful exercises to practice different tenses

SIMPLE PRESENT

1. http://www.eclecticenglish.com/grammar/PresentSimpleToBe1A.html
2. http://www.ego4u.com/en/cram-up/grammar/simple-present/form/exercises
3. http://www.englisch-hilfen.de/en/exercises/tenses/do_does.htm                                                                       

4. http://kidseslgames.com/grammar%20games/Present%20Simple/presentsimple1.html

5.http://www.eslgamesworld.com/members/games/vocabulary/hangman/Present_Simple_Hangman1.html

PRESENT CONTINUOUS

1. http://www.eclecticenglish.com/grammar/PresentContinuous1F.html

2. http://www.englishpage.com/verbpage/presentcontinuous.html 

3. http://www.englishpage.com/verbpage/verbs1.htm

4. http://www.englishpage.com/verbpage/verbs2.htm

5.http://www.eslgamesworld.com/members/games/grammar/present%20tenses/present%20progressive%20hangman.html

6.http://www.eslgamesworld.com/members/games/grammar/present%20tenses/present%20tenses%20snakes%20and%20ladders.html

GERUNDS

1. http://www.ego4u.com/en/cram-up/grammar/infinitive-gerund/exercises?21

2. http://www.tolearnenglish.com/exercises/exercise-english-2/exercise-english-57520.php

3. http://wwwedu.ge.ch/cptic/prospective/projets/anglais/exercises/gerund1.htm

4. http://wwwedu.ge.ch/cptic/prospective/projets/anglais/exercises/gerund2.htm

5. http://www.englisch-hilfen.de/en/exercises/structures/gerund_infinitive.htm

PAST TENSE

1. http://www.bradleys-english-school.com/online/concentration/past2.html

2. http://www.ego4u.com/en/cram-up/grammar/simple-past/exercises?04

3. http://www.ego4u.com/en/cram-up/grammar/simple-past/exercises?05

4. http://www.ego4u.com/en/cram-up/grammar/simple-past/exercises?06

5. http://www.marks-english-school.com/games/b_past.html