ますます

The word ますます can be used with verbs, adverbs, and the adverbial forms of adjectives to indicate that something is happening to an even greater (or lesser, if negative) degree than before. It often translates as something like "more and more" or "ever -er", depending on what it's used with.

Note that ますます cannot be used with "future controllable actions", as Tobira calls them. An example of such a sentence would be ますます頑張って下さい. The word もっともっと would be appropriate there instead.

漢字を覚えれば覚えるほど、単語の数がますます増えて、ますます日本語が分かるようになりますよ。
The more kanji you learn, the more the number of words increases, and you become more and more able to understand Japanese.

リーさんは毎日ジャネットと会い始めて、ますます嫌いになったんだ。
Lee-san began to meet with Janet every day, and he grew to hate her more and more.

歌の次にダンスが始まりました。すると、ますますたくさんの人が集まって来ました。
A dance started with the next song. Then, more and more people came and gathered.

田中がクラスにもう勉強しなかったから、クラスはますます難しくになったんだ。
Tanaka didn't study anymore for class, and so class became more and more difficult.