Trimming sails on a ketch is like most boats you start at the bow and trim aft. Ketches generally are pretty low tech rigs with wide shroud bases. As a result it is pretty hard to very hard to over trim a genoa on a ketch upwind. Next comes the main which should be trimmed so that the Batten teletales flow. Since the mizzen represents a sizeable percentage of the overall sail plan, you need to be careful upwind not ot over trim the mainsail and dump extra turbulent air on the mizzen. Mizzens often end up being over trimmed to take the luff out. A little luff can be tolerated.

As the breeze bulds the mainsail traveler should be lowered to leeward and the genoa lead moved slightly aft.

As you crack off of the wind, a ketch begins to come into its own. It is important not to overtrim the sails on a reach. Use you vangs in the mainsail and mizzen as twist generally means that the foot of the sail ends up being too tight and sends back too much dirty air onto the mizzen.

Once you start to broad reach the mizzen begins to blanket the mainsail and theirs not much you can do for it except rig a mizzen staysail.

As every one noted, in heavy air you can drop the mainsail and sail jib and jigger. Most ketches will hove to Jib and jigger as well.

Jeff