In English, we would say "the more you practice, the better you will speak German." In German, these types of parallel comparatives are called Proportionalsätze, and are constructed as follows:
Je + comparative adjective (phrase), desto or umso + comparative adjective (phrase).
Take a look at the examples below, paying special attention to the positions of the adjectives (or the words mehr or weniger) and the verbs in both clauses.
Und je positiver das ausfällt, desto motivierender.
And the more positive that is, the more motivational.
Caption 65, Gamification - Wie Spielen den Alltag interessanter macht
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Je niedriger die Regionalklasse, desto günstiger wirkt sich das auf den Versicherungsbeitrag aus.
The lower the regional classification, the cheaper it makes the insurance payment.
Captions 10-11, Kfz-Versicherung - Was ist die Regionalklasse?
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Denn je kälter es wird, desto weniger Zeit dürfen sie draußen sein.
Because the colder it gets, the less time they're allowed to be outside.
Caption 4, Im Zoo - Tiere im Winter
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Je mehr Energie ich spare, desto weniger muss ich auch jagen. So einfach ist das.
The more energy I save, the less I have to hunt. It's that simple.
Caption 17, Für Tierfreunde - Geparden
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Ja, und je braver wir zum Hund sind, desto mehr macht er, was er will.
Yes, and the nicer we are to the dog, the more he does just what he wants.
Caption 25, Haustiere als Geschenk? - Vier Pfoten unterm Weihnachtsbaum
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Often, you will see the word umso rather than desto.
Aber je mehr uns davon gelingt, umso besser.
But the more it succeeds for us, the better.
Caption 31, Angela Merkel - beim Nachhaltigkeitsrat
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Je eleganter man wirkt, umso mehr wird man auch anerkannt... gesellschaftlich, beruflich...
The more elegant one appears, the more one is also accepted... socially, professionally...
Caption 42, Auf dem Laufsteg - Modelcollege in Wiesbaden
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Further Learning
Based on the structures you see above, make up your own sentences with je and desto / umso. If you need some comparative adjectives to get you started, you can find a few helpful tables on this page. You can also visit Yabla German and look for further examples.