Like English good, better, best, German has a handful of irregular comparisons — and they're among the most used words in the language:

Adjective	Comparative	Superlative	English
gut	besser	am besten	good, better, best
viel	mehr	am meisten	much, more, most
gern	lieber	am liebsten	like, prefer, like best
groß	größer	am größten	big, bigger, biggest
hoch	höher	am höchsten	high, higher, highest
nah	näher	am nächsten	near, nearer, nearest

Most other adjectives are regular: schön → schöner → am schönsten, klein → kleiner → am kleinsten. After -t, -s, -ß or -z the superlative usually adds an -e-: am ältesten, am kürzesten — am größten is the odd one out.

Mehr never takes an ending: mehr Zeit, mehr Freunde.