Obviously slowing down using any means helps but the best way to recover is as the 'down' wing starts to rise apply full into down wing aileron and back to neutral. Wait for the wing to go 'down' again and repeat the action. After about four cycles the rolling motion begins to dampen out and normal roll control becomes effective. If you're good you can work both wings but it requires very good co-ordination. During my initial Command training we had to be familiar with Dutch Roll recovery but only in the Sim. If my memory serves me correctly in the early days they lost a 707 trying it in the aircraft. Quite a strange aerodynamic event the first time you see it. Good to know the limits of the envelope we don't seem to 'explore' this enough these days.