Yeah, like Redeye said. Your TM entrance will vary based on the layout of your store. Ours is directly next to the regular store entrance, which can sometimes be a problem if there are guests waiting outside who seem to think they can get in with the other Team Members... Anyways, at my store there is a little brass button that acts as a doorbell that chimes over the PA to let the LOD know that someone is at the employee entrance. That may or may not be unique to my store, I'm not sure.
Definitely arrive early. I've lost count of the number of times I have been late to an opening GSA/Service Desk shift because the LOD was slow to let me in. As far as cashiering goes, it's basically the exact same as any other shift except that you're there at what to me is an ungodly hour. It'll usually be dead quiet for the first hour or so. If we have a spare cashier or two we will have them push candy/zone the checklanes while they wait for guests.