Communication with the driver is important when getting on and off the bike as a passenger. Usually, the driver will get on first, but yours may prefer to jump on second. Either way, you should both be aware of exactly how the other person will mount the bike.
Always tell the driver when you're about to hop on the motorcycle. You might want to use the driver's body to steady yourself, which is fine as long as they know it's coming. Some people use the foot peg as a step while others just swing their legs over.
Getting off the bike is basically the same deal. Communication with the driver is still important because you both need to know who gets off first.