found this interesting page with some advice on how to become a polymath. There are also links to Baldassare Castiglione‘s Il Cortegiano – a Renaissance self-help manual that introduced the idea of the Renaissance Man or uomo universale.
Castiglione was an Italian courtier and diplomat – and one of the last Italian Renaissance Humanists – who spent sometime in the Spanish court of Charles V, Holy Roman Emperor. There, he probably met with Spain’s greatest Renaissance Man, poet and soldier Garcilaso de la Vega. Garcilaso was a friend of Castiglione’s Spanish translator, Catalonian poet Juan Boscán Almogáver.