Yes, the most important rule is don't send beer via US Mail. If you are going to send beer, I mean yeast samples, it is recommended to use FedEx or UPS. Also, I like to double box. That is, I put the bottles in a box with cushioning, then put that box inside another box with cushioning. The means that even if the outer box is breached (which happens) the bottles still have a good chance of surviving the trip.
Also since sending multiple bottles can tend to get heavy, I save and reuse those big puffy plastic air packets, as they are very good at cushioning and weight almost nothing. Lowers shipping costs dramatically. And I also wrap each bottle in bubble wrap.