The aim of hyphenation is usually to make things easier to read. In general, if the two words modifying the noun appear before it then they should be hyphenated. If they are post-modifiers then the hyphen is not necessary.
Here’s an example:
‘She was a well-known scientist.’
‘The scientist was well known.’
Hyphens can also be helpful in demonstrating that the two adjectives are combined.
A ‘first-class discussion’ is quite different from a ‘first class discussion’.
“Oh, you want to see a man-eating plant.”
There are exceptions to any rule, for example if the left modifier has an -ly ending and the right modifier has an -ed then they are usually not hyphenated e.g. ‘a distantly related cousin’. Compound modifiers with comparatives or superlatives are generally not hyphenated either e.g. ‘the most recent change’.
If you’re not sure, check a dictionary or ask a proofreader.
Comparatives are used to compare one thing to another- they often have an ‘er’ ending. Superlatives are used to compare more than two things- they often have an ‘est’ ending. So ‘Holmes is better than Watson’ (because there are only two of them) but ‘George is the best character in the Famous Five’ (because there are more than two of them).
A common error is using the superlative when there are only two things in contention:
‘Of the two methods, the oldest was better’ should be ‘Of the two, the older was better.’
Double comparisons are also not acceptable in standard English:
‘She was the most greatest’ should be ‘She was the greatest’.
‘She is more faster’ should be ‘She is faster.’
Additionally, I also see ’empty comparisons’, the use of a comparative without a base:
‘Today was better.’ Than what? It should be made obvious to the reader what you are comparing.
Also, superlatives are often over-used in writing. Unless used stylistically, exaggeration can become a barrier to how much the reader will understand and trust your statements. Think of the number of times advertisers use superlatives- do we really believe that their product is ‘the best’?
Not all multi-syllable adjectives take ‘er’ and ‘est’. This is where ‘more’ or ‘most’ is used before the adjective.
For example ‘The sofa was the most comfortable seat in the room’.
I hope that’s helped. Let me know what you think or if there’s anything else you’d like explained or discussed. As always, I’d very much appreciate if you could share or like this if you found it useful! Thanks!