It rather depends on which lab you are going in for placement. If you already know what discipline you will be going for then read up on that. If you are currently unsure then what the laboratory manager will be looking for is somebody who is keen, intelligent, well mannered and seems nice.
I realise that these are relatively generic qualities for any interview but then you are only going for a years placement and you will not be expected to know too much. Just be likeable.
If I can help with any further questions then please do ask. I am an experienced BMS in Microbiology.