Most adjectives follow one of these rules when making comparatives.
New becomes newer
Intelligent becomes more intelligent
pretty become prettier
Clever becomes cleverer
Simple becomes simpler
Yellow becomes yellower
There are also irregular adjectives which don't follow set rules. Here are the most common.
The book was better than the movie.
I'm feeling much better today than yesterday.
The weather is getting worse and worse.
She ran farther than the rest.
I want to further my understanding of computers.
I have less time than usual.
I have a small bag. It's smaller than yours.