Big
Small
Tiny
Tall
Fat
Thin
Smart
Stupid
Strong
Weak
Tidy
Messy
Dirty
Clean
"Higher" is the comparative of high. The superlative is highest.
lazier and laziest
'Next' is a superlative; it means 'nearest'. The positive is therefore 'near' and the comparative is 'nearer'.
harmful
last
easier and easiest
The comparative form of rude is ruder, and the superlative form is rudest. It is common to form the comparative and superlative of short words like this by adding -er and -est.
busier, and busiest
stronger and strongest
older, oldest
finer, finest
For words of two syllables not ending in y, use more for the comparative and most for the superlative.