Whoever said "us elots of overheads" - DON"T!
whenever people in my tutes used heaps of overheads, they got marked down for having more or less irrelevant/pointless overheads that didn't add to the presentation... not to mention the waste of money....
You don't have to use a powerpoint presentation system - sometimes it's better not to as you have to book it ahead of time and if it stuff's up you'll lose marks for not getting the presentation done.
I've gotten HD"s with just overheads... i never used powerpoint and i've never gotten lower than a D for tute presentations - so it's not necessarily better. it takes a lot more time and organisation.
Make sure you DON"T just reitterate the readings or lecture notes or seminar guide or whatever because you won't get a good mark - you need to be original. Get the class involved even if it's just by asking them questions here and there or give them a 5 minute activity to do - giving food as a 'reward' always helps as if you get stuck with a bunch of boring people they won't be likely to contribute, especially as in the 1st few weeks you probably don't know each other too well.
Make sure you know your stuff!!! Be prepared to be asked on the spot questions and have intelligent sounding answers up your sleeve.
Don't! just read what you have on the powerpoint/overhead - these slides should have minimal information - try to stick to bullet pointe, t ables, graphs, diagrams and rather than put up what you want to explain - use the diagram to show what the thing is and then explain it yourself.
If you have to do a handout - make sure it's concise but not too simplistic. DOn't pack the page/s full as if it's an essay - use dot points, headings, tables, put questions for students to consider, put references (if applicable) etc
And try not to sound like you're as bored as the rest oft he class probably are because these preentations can get a bit monotonous so if you seem motivated, tutor's tend to have a positive view of how your preentatino will go before you start