The file system is a good place to start since many externals arrive with FAT32 formatted volumes which can vanish on power loss. Why not use Apple's File System to avoid that?
Next we have the old problem of backup. Externals are not reliable. Those that don't backup learn eventually why we can't go without.
I had an external hard drive plugged in via USB to my Mac when someone accidentally bumped the power switch on my power strip and shut everything off. I unplugged the power cord to the external drive and booted up the Mac. The USB cord from the external drive to the Macis still plugged in and the power switch on the external drive is still set to on.
I am wondering: is there any specific order of steps I should take when starting up the external hard drive in order to minimize the chances that there will be data loss on the external drive?