Before everything you must study the basics of the English lan.guage if this is okay,
first of all, you need to listen to the English accent carefully because its so important to differentiate between accents, the second thing to do is to understand the meaning, not the words particulary, and if you don't understand the meaning so you need more vocabulary, it is suggested to learn everyday a new word, it looks very few but in fact it's great, look with me, there are 356 days in a year, so what if you learn everyday a new word, how many words will you get in a year ? 356 words, isn't it amazing ? well I know it is, what is needed is simple, one word Patience
the last thing to do to understand someone speaking English is understanding the form of words how they are prononced in each accent, it deffers but once you get it, it becomes easy.
well this is only an opinion
if you have more things to share, everything is welcome