Study Irregular Verb Tables - As the old saying goes practise makes perfect!
Listen and identify the practical use of 'Tenses' in real English

Vocabulary:

• Make a point of learning the vocabulary of particular topics that are of interest to you.
• Build your own vocabulary with word families (collocation) for your own reference.
• Practise pronunciation and this will help you to improve your understanding when you hear others talking about the subject

Set yourself a target for new words every week. When you learn a new word try to use it as soon as possible that way you’ll remember it - Use it or Lose it!

Surround yourself with English

• 'Tune in' to English wherever and whenever you can. Listen to songs, learn the lyrics, and keep up with news programmes - regular news bulletins with stories often repeated throughout the day are good for becoming familiar with language.
• ‘Phone In’ radio programmes - where members of the public call on the telephone, are a good way to hear real people and learn to recognise 'regional accents'. If you lose concentration and ‘switch off’ after listening for a long time - perhaps during a radio play try not to give up but ‘switch’ on again by listening for key phrases/ words.
• To help you understand what they’re talking about try to listen for verbal clues - words and phrases you recognise.
• Using your own knowledge of the subject try to work out what they have said and what you might expect to hear next.
• Understanding  jokes - A funny story told in English is a really good test of ability but don’t worry or be put off if you don’t always ‘get’ (= understand) the ‘punch-line’ of a joke(= the end of the joke).
• If you are not living amongst English speakers and it is difficult to immerse yourself in the language - try to set aside time for regular practise. Perhaps have a daily ‘English hour’ when you communicate with friends and or family only in English. Speaking on the telephone, perhaps to work colleagues, is a particularly good exercise as without non verbal communication you will have to rely on Listening and Speaking skills.

Most importantly, don’t be too hard on yourself - try to enjoy and remember:
...slow steps are better than no steps!