Put mobo on top of foam packaging
Remember to put standoffs in case
Put mobo in case
You might have to put your HDD, DVD and PSU in case before putting mobo in, see how much room you have and what angles things need to be slotted in before hand
You might want to hook up your 4/8 pin mobo power cable before putting mobo in case because it's often tricky after.
Hook up all your PSU/SATA/PowerbuttonEtc cables
Install GPU, plug PCIe power cable into GPU