Learn German by playing
Four characters English does not have, nouns that all take a capital, and compound words that go on for a while. Those are the three things to practise, so those are the three things here.
Play in GermanUmlauts change the word
Schon is already; schön is beautiful. Mutter is mother; Mütter is mothers. The umlaut is not an accent you can drop — it is a different letter, and often a different meaning or a plural. ß is its own case: it follows long vowels, where ss follows short ones.
Capitals count
German capitalises every noun, so the games here are case-sensitive: Haus, not haus. It is the habit that most marks out someone who has written German from someone who has only read it.
The long ones
Krankenhaus, Straßenbahn, Geschwister, Frühstück. Compounds are where German gets its reputation, and they are far less frightening once you have typed a few dozen.