ば～程(ほど)The more…the more

ほど (sometimes written in kanji as 程) has the basic meaning of 'extent'. ば〜ほど shows a proportional relationship, similar to 'the more (A), the more (B)', e.g. 練習すればするほど上手になる ('The more you practice, the better you get.') When used alone, ほど means 'so much that (A)' or 'to the extent of (A)', e.g. 驚くほど静かだった ('It was quiet to a surprising degree.' / 'It was so quiet that I was surprised.')

どんどん is an adverb that implies rapid or dramatic change, often in leaps and bounds, e.g. どんどん大きくなる 'grow rapidly'. 〜ば〜ほど is a structure that shows proportional change, like 'the more (A), the more (B)' in English. For example, 大きくなればなるほどいい ('The bigger it gets, the better.').

Both can be used to describe change, but with different patterns. ば〜ほど expresses a proportional relationship between two things, like 'the more (A), the more (B)', e.g. 練習すればするほど上手になる ('The more you practice, the better you get.') 一方だ shows a continuous, one-way change in a single direction, e.g. 物価は上がる一方だ ('Prices just keep rising.')

They are similar in that both describe change, but ば〜ほど specifically expresses a proportional relationship between two things, like the English 'the more (A), the more (B)', e.g. 見れば見るほど好きになる ('The more I look, the more I like it.'). In contrast, ますます simply emphasizes continued intensification, e.g. 彼の人気はますます高まっている ('His popularity is steadily rising.')

ば is a conditional form that emphasizes the condition needed for a result, e.g. 勉強すればうまくなるよ ('If you study, you'll get better.'). ば〜ほど builds on this to mean 'the more (A), the more (B)' e.g. 勉強すればするほど、うまくなる ('The more you study, the better you'll get.').