Getting there early to see about lighting is a good suggestion, above. There are two general philosophies in events, reportage and posed. For any presentations or talks, take a few of the speakers in context(reportage), with the 70-200. The most shots of such an event will probably posing small group as they socialize. This one takes being a little more assertive and asking people to pose because wandering around taking photos of people in small groups will result in at least one person looking awkward or with a bad angle so don't waste time waiting for everyone in the group to be naturally photogenic or or not looking goofy. For this you will want the 17-55 getting close enough to fill the frame but not too wide of angle so there is distortion. Shooting wider angle with people at the edges of the frame, which renders them in an unflattering distorted way. Be sure to get at least one good image of each person in either groups or solo. Get a member of the group who knows everyone to volunteer to record the names of the people in the photo. They can write them in a note book while shooting while you call out the frame number. This works better than afterwards because in case they do not know someone, you can ask them for their names. This saves a lot of time when they seek to publish the images. Lighting for the small groups is easy with a diffused flash but the reportage type shots of the proceedings will be a challenge for lighting unless you can set a few slave up that can bounce off good surfaces. Since you will likely be shooting without flash for this portion be sure to fill the frame with the subject so you do not have to crop, which reduces res and signal to noise ratio of higher ISO shots in ambient like.