Selected web guides:
Scripts from Brigham Young University has guides and tutorials to handwriting from a variety of historical time periods and places
Paleography Toolkit from Notre Dame; focuses mostly on Western European historical scripts.
Facsimiles (reproduced manuscripts):
Facsimiles of manuscripts published as books are useful for practicing, especially if they include transcriptions. Search a library catalog by country and the term facsimile.
Representative manuals published as books:
English Handwriting, 1400-1650
古文書くずし字見わけかたの極意 / Komonjo kuzushiji miwakekata no gokui