What instrument do you play? I am a firm believer that a conductor should have worked deeply in the music of some instrument. A knowledge of the piano (if this is not your primary instrument) is also most important. Often young conductors think they must play every instrument in the orchestra. This is nonsense. What is important is a theoretical knowledge of the different instruments. (The best book on this, for me, is A. Casella and V. Mortari’s La Tecnica dell’ Orchestra Contemporanea, published by Ricordi. I do not know whether it has been translated; I have the second edition published in 1950.) In addition, a detailed study of harmony, counterpoint, score reading, and musical analysis are indispensable. A deep knowledge of the repertoire and stylistic practices of the different composers is also essential. As with any other endeavor, the more general knowledge you bring, the better.