Practise!

A very funny game: http://www.macmillandictionary.com/verb_wheel/
And more:
http://www.englishpage.com/irregularverbs/interactiveirregularverbs1.htm

http://www.ego4u.com/en/cram-up/grammar/irregular-verbs

http://www.vedoque.com/juegos/juego.php?j=English-Irregular-Verbs&l=es


http://www.engames.eu/irregular_verbs/withFluencyMC/Irregular%20verbs%20with%20Fluency%20MC%204%20(Web)/index.html