Monitoring students in the lab
There’s one obvious way: to send a signal that lab presence is important, the research group leader and permanent staff must be more present in the lab. Most students are looking for opportunities to increase interaction with professors and advisers, thus by being “accessible” in the lab for discussions, you will increase lab presence. In addition to inciting students to come, that will be a even greater stride toward “cooperation and discussion among lab members”.

This also works with post-doc and the more experienced grad students: you need to avoid the idea that “lab presence” is only for the newbies, while the grown ups get out of there as often as they dare!