A few online free books websites :
... PRACTISING your GRAMMAR :
>>> grammar quizzes, from beginning to advanced levels
>>> Quizzes on the BBC site
>>> MCQ : Present perfect or past simple/preterite ?
An MCQ is a test that includes Multiple Choice Questions.
... PRACTISING irregular VERBS
-did I hear "Ouch !" ?
Actually there are no other solutions than learning them by heart.
You all have a list of these verbs in your textbook : such lists
are often at the end of the textbook.
Here is an IRREGULAR VERBS BASIC LIST
click on the PDF logo ^^^
with different groups of verbs, according to their changes.
This list is quite a "basic" one : it includes only the most common verbs,
the verbs you MUST absolutely know.
My "Here is a basic list" means... you must regularly brush up <<<
on many other verbs :o)