=> Use a headset
=> Cut out all distractions on your end, like other phones ringing, kids, dogs etc.
=> Send good instructions to participants well prior to the call, telling them to mute their phone, no speaker phones, use a headset, cut out distractions, your policy on questions, etc.
=> Be very clear about start times and time zones so that people don't call in too early or too late.
=> Make handout and printed material downloadable. This saves you printing an mailing and if you do it right, any links you put in the handouts can be clicked on by the participant.
=> Tape the seminars to critique yourself and to create instant products.