The dh and th Sounds, and the a That Sounds Like o
Javanese has two pairs of consonants that Indonesian lacks. Plain d and t are made with the tip of the tongue against the back of the upper teeth. Dh and th are made with the tongue tip curled slightly back towards the roof of the mouth. To a beginner the difference sounds tiny, yet it changes meaning: wedi means afraid, while wedhi means sand. Words such as bathuk (forehead) and kathah (many, in krama) only sound right once the th is made with that curled tongue.
The second surprise is the letter a in open syllables. In the Solo and Yogyakarta accent, lara (sick) is pronounced close to loro, sega (rice) close to sego, and the word Jawa itself comes out as Jowo. Standard Latin spelling keeps the a. Learners who read words exactly as written sound stiff, and learners who spell words the way they hear them make mistakes on paper, so both habits need training at once.
Minimal pairs are the quickest drill. Say wedi and wedhi one after the other, record yourself and compare the recording with a native speaker. For the vowel, read a short word list twice: once as spelled, once as people actually say it. You have it once a short sentence comes out aloud with no hesitation over each d, dh, t and th.
Drill wedi against wedhi until your tongue sorts them on its own, and say a as o wherever native speakers do.