A good dasha usually can be seen in the birth horoscope sitting in a favorable house from the lagna, in good dignity and with conjunctions or aspects of manifesting or benefic planets.
But also you can look at the dignity of the planet in the shastiamsha. This will be the most telling in whether or not it´s gonna be a good dasha or not.
If a planet is debilitated in the D60, it won´t be helped in any other varga. It might be better in other vargas but the D60 is always the final say.
If a planet is Exhalted in the shastiamsha it won´t be let down during it´s dasha by other planetary positions of it in the other vargas because it still has the final say.