The reason that your preceptor knows what is going on all the time is probably because she has been doing it WAY longer then you have. I felt the same way when I started out but I soon started learning what test went with what labs, when patients would usually go for certain tests, and so on. For me it came with time, doing it over and over again, and finding the pattern behind orders, tests, and procedures. If it makes you feel better you can come in early to look at the charts but I bet with time its going to start clicking like it did for me.