Hazrat Hakeemul Ummat Moulana Ashraf Ali Thanvi ra recommended following tips for waking up early;
1. Eating less at dinner
2. Eating dinner earlier (ideally before esha)
3. Drinking less water (in evening)
4. Reciting the last 4 veses of surah Kahaf (18:107-110) once (at bed-time).
Basair Hakeemul Ummat page 562
Also, to have a sincere intention for this and make dua (prayer) asking for Allah swt’s help to arise at the specific intended time.