Hey!
I used to help a lot of people with their English homework. And the most striking mistakes are still caused by the wrong use of verbs and their tense (past, present etc.) I came across this site and if you want to practice your verbs this might be pretty helpful!
http://www.englishpage.com/verbpage/verbtenseintro.html
Moreover, of course talking to native speakers is a lot of help too. usually they can correct you, which also helps a lot!