Comparative and historical linguistics offers some clues for memorising the accent position: If one compares many standard Serbo-Croatian words to e.g. cognate Russian words, the accent in the Serbo-Croatian word will be one syllable before the one in the Russian word, with the rising tone. Historically, the rising tone appeared when the place of the accent shifted to the preceding syllable (the so-called "Neoshtokavian retraction"), but the quality of this new accent was different – its melody still "gravitated" towards the original syllable. Most Shtokavian dialects (Neoshtokavian) dialects underwent this shift, but Chakavian, Kajkavian and the Old Shtokavian dialects did not.
Try to answer this question if possible (otherwise reply "unanswerable"): What offers some clues for how dialects were different?
unanswerable