Word qualifying a noun or pronoun is called an adjective.
1. The adjectives ending in -ior (prior, junior, senior, superior, inferior, posterior) take "to" and not "than" after tehem.
e.g. He is senior to me.
2. Some adjectives like unique, ideal, perfect, extreme, complete, universal, infinite, perpetual, chief, entire, round, impossible are not compared.
e.g. It is the most unique book. (wrong)
It is a unique book. (correct)
3. Comparative degrees is used in comparing two things or persons.
e.g. It is the better of the two books.
Superlative degree is used in comparing more than two things or persons.
4. Double comparatives and double superlatives must not be used.
e.g. He is more wiser than his brother. (wrong)
He is wiser than his brother. (correct)
5. When we compare two qualities in the same person or thing, the comparative ending -er is not used.
e.g. You are wiser than old. (wrong)
You are more wise than old. (correct)
6. When two adjectives in superlative or comparative degree are used together, the one formed by adding "more" or "most" must follow the other adjective.
e.g. He is more intelligent and wiser than his brother.(wrong)
He is wiser and more intelligent than his brother.(correct)
7. When tow adjectives with differing degrees of comparison are used they should be cojmplete in themselves.
e.g. He is as wise, if not wiser than his brother.(wrong)
He is as wise as if not wiser than his brother. (correct)
8.When two changes happen together, comparative degree is used in both.
e.g. The higher you go, the cooler you feel.
9. When comparative degree is used in superlative sense, it is followed by "any other".
e.g. Kapil is better than any bowler. (wrong)
Kapil is better than any other bowler. (correct)
10. Compund adjective formed by adding "worth" is placed after the noun it qualifies.
e.g. This is a worth seeing sight. (wrong)
This is a sight worth seeing. (correct)
11. When two or more comparatives are joined by "and", they must be in the same degree.
e.g. Russel was one of the wisest and most learned men of the world.
12. When there are two objects of comparison, then to avoid repetition of noun, "That" is used ofr singular noun and "those" for plural noun.
e.g. The climate of Ranchi is better than Gaya (wrong)
The climate of Ranchi is better than that of Gaya. (Correct)
13.If comparison is made by using "other" , "than" is used instead of "but".
e.g. He turned out to be no other than my old friend.
14. Likely, certain and sure are followed by "to".
e.g. He is likely to win.