Make your own gap-filling exercises from English texts.
Choose a short, interesting English text that is not too difficult (e.g. lyrics, text from your textbook, news, excerpt from a story/novel). Copy the text and delete some words in the copy, e.g.:
- prepositions
- adjectives
- verbs in a certain tense
Try to fill the gaps correctly and then take the original text to check your answers.
This sure is more fun when doing it with friends. Everyone prepares a short text and gives a copy to the others, who will try to fill the gaps correctly.
To make things a bit easier, you can provide the words in a different order or as a translation.
Practice makes perfect.