Many English language learners find the uses of so and such a complete mystery, however, the rules for using so and such are very clear and straightforward:
If you are using it before an adjective or an adverb, use so, e.g;
If you are using it before a noun or noun phrase, use such, e.g;
There are, however, one or two exceptions to the above rules, and they are:
If the noun follows little, few, much or many, you will need to use so, even though you are using a noun or noun phrase, e.g;
One important thing to remember is, that in writing, you should only use so or such if you are using 'that' after it. This is because so and such are used for emphasis, which can be expressed in spoken English by intonation, where the word so or such is said with emphasis. But in writing, it is difficult to show emphasis unless you use 'that' plus a clause. If you don't use the 'that' clause, you shouldn't use so or such, but 'very'. For example:
Of course, you can use 'very' instead of so and such whenever you want to, but it is good to use a range of vocabulary, and it will give you more marks in examinations because you will be using different syntax, which means that you are not repeating vocabulary. So use a variety of different ways of saying the same thing, and get those higher grades.