There are two constructions you may use. The first is this. The comparative adjective plus (plural: plures, plura), which means "more", combined with quam ("than"). The two things being compared are put in the same case. In the first, third, and fourth sentences, the subject "He" would be in the nominative, thus "suus amicus" follows suit.
In the last two sentences, I use magis and maxime instead of plus, since we need an adverb instead of an adjective.
- Plures libros quam suus amicus legit. (He reads more books than his friend.)
- Hic est qui plures libros habet. (He is the one who has more books.)
- Plus saccharum quam suus amicus edit. (He eats more sugar than his friend.)
- Magis quam suus amicus legit. (He reads more than his friend.)
- Hic est qui maxime legit. (He is the one who reads the most.)
You could also use the ablative of comparison. In this construction you omit quam. This is what the quam-based sentences would look like using the ablative of comparison.
- Plures libros suo amico legit.
- Plus saccharum suo amico edit.
- Magis suo amico legit.
You can read about both constructions in sections 406-407 of Allen and Greenough.