From SecularPortal

Talks are easy to organise as they generally only require one person and the equipment required, if any, is usually already available in the conference facilities provided by your university.

Guest speakers

Guest speakers are great to bring in as you can bill them as a big name. This works especially well if they are someone at your university as usually they have letters before and after their name and so it sounds big and important when actually they're already on campus.

It's good practice when bringing someone in to give a talk to make sure there is water available during the talk and to invite them to the pub to buy them a pint afterwards, particularly if you're not paying expenses.

Best practice

Sometimes the speaker will want to use some kind of presentational devices and so it's advisable to arrive at the venue early (and book it from well before the event actually starts) to get down there and test the computer systems and projector to make sure everything is working.