The 据 reading dominates: 根据 (based on), 据说 (it's said), 数据 (data), 证据 (evidence), 占据 (to occupy). All news-report openers and citation phrases (据悉, 据称, 据报道) use jù.
mistakes
There is one - and only one - common word where 据 takes the first-tone reading jū: 拮据 (strapped for cash). Everywhere else 据 is jù. If you see 据 in any compound that's not 拮据, read it as jù.
history
Simplified from the traditional form 據, whose right side was the phonetic 豦 (a tiger-and-boar graph). The PRC reform replaced that complex right element with 居 - visually simpler, and a near-rhyme that hints at the modern jù reading.
Left hand radical, indexing component (variant of 手). Marks 据 as a hand-action character: gripping, occupying, seizing - hence the abstract sense 'to rely on, to base oneself on.' Same radical anchors 抓 (grab), 持 (hold), 拿 (take).
Right-side 居 supplies the sound - jū shifts to jù with a tone change. A faint semantic echo helps too: what one resides in is what one occupies. This is a simplification artifact: the traditional form 據 used 豦 as the phonetic, which the reform swapped for the easier-to-write 居.
