If you've asked your students to complete some readings or activities prior to the lab you would be wise to find out whether they have done so. You can do this in a variety of ways, e.g., asking a few pointed questions or having students break into small groups for 10 minutes at the beginning of the lab while you circulate, asking for questions that students may have about their preparations. AND it's costly to conduct, you may need to reschedule the lab. Otherwise, you can use this informal assessment to clear up areas of confusion before the lab gets underway. This should serve to eliminate the unnecessary breakage or repetition of common questions about a particular piece of equipment.
Handouts can be efficient aids for a weekly lab.
Make and use them creatively. This can be done with a handout, with words, or by referring them to the appropriate page of a lab manual. Again, taking the time to anticipate difficulties before everyone starts working may save you from providing countless repetitions of a minor procedure. You should also adhere to the rules since students view you as a model for lab behavior. Making safety concerns known is a necessary first step in avoiding serious problems.