There is no particular order of installing a computer in a case…but after doing it more times than I can count, I usually like to install as much as I can prior to installing the motherboard. I guess mainly to keep from bumping the large CPU cooler I usually have installed.
Always first install the I/O panel that came with your motherboard. Do it first to keep from forgetting it. I have forgotten, more than once. It sucks, because you don't realize it until you plug the cables in.
Next, install the offsets. You may need to set your motherboard in the case to judge where the offsets need to go. Every motherboard I have owned had the screw holes in the same place. The offsets that are included with the Blackline are nice. I have seen several different sizes, the ones that use the smallest screws are likely to strip out. These offsets use larger screws. Another cool thing is that the offsets and their intended screws are in the same zip lock bag. Normally, they are dumped into the same bag as all of the other screws, and you have to dig around to try to find enough of the proper screws.
After that, I usually install the drives. Place the locks on the sides of the hard drive, and simply slide the drive into the bay. It locks tight.
Remove the bezel, place the locks on the side of the optical drive, and slide it in until it locks. Replace the bezel. It's a pretty tight fit, so you may have to work it around a little.