Ask questions! As someone who works in a lab full-time, I would much rather answer seemingly simple questions than fix a big mishap. Introduce yourself to everyone in the lab and get a feel for everyone's role in the lab. Ask about what hours people keep in the lab, where people eat/store food, access to the lab, what equipment is fair game and what shouldn't be messed with. Read publications that the lab has produced. Ask about how the lab keeps notebooks and/or digital data storage. You should also ask if you need any special training (animals, humans, radioactivity). Show curiosity and ask or research on your own how each assay or experiment you perform works. This is one way to help get a good LOR. Hope this helps!