In general, when you get in a volcanic ash cloud, the trick is, to get out as soon as possible (obvious), and to keep the engines running.
To keep the engines running, you need to get the temperature down inside the combustion chamber and turbine, and make the engine less succeptable (hope I spelled that one correctly) to stall. The way to achieve this is to get the thrust levers to idle, and extract as much bleedair as you can from the engines, in other words, WAI on, TAI on and the packs in "high".
Regards