Some of the ways that you can improve your English are simple. Some expressions mean exactly the same thing and/or can be used in the same context but they’re seen as more advanced to examiners who are scoring you on your level of English.
For example, “many”, “much”, and “a lot of” are all synonyms. You probably already know that the difference between them is grammatical. We use “many” with countable nouns such as “pen” and “paper” whereas we use “much” with uncountable nouns like “air”, “time” and “money”. Then there’s “a lot of”, which you can use with both countable and uncountable nouns. There is another expression, however, that is seen as being more advanced but can be used in the exact same context as “a lot of”. The next time you say or write something, try using “a great deal of” instead of “a lot of”.
I don’t have a lot of time to talk to you – I don’t have a great deal of time to talk to you
I found a lot of pens in the drawer – I found a great deal of pens in the drawer