The rule: the most or the least + adjective + noun. But pay attention to the exceptions...
1/ It is (big) company of the town.
2/ This tiny car is (expensive) car of their range.
3/ It is (difficult) decision I have ever made.
4/ Is the Nile (long) river in the world?
5/ He bought her (beautiful) necklace he could find.
6/ I fell asleep: it was (boring) film ever!
7/ Football is (popular) sport in Italy.
8/ That shop assistant is (polite) one I know!
9/ He must be (bad) cook I have ever met...
10/ It is (far) place we have travelled to.