Building a computer by myself. Any suggestions?

1. Remember to unplug your computer before messing around inside of it... Line voltage is present in 'off' power supplies, ethernet cables, monitor cables, and even usb cables. Though chances of such a voltage causing damage there still is a chance that something may fry when you're moving things around each other.

2. Watch out for older SATA drives.. the cables have a really, really, really, poor locking mechanism and they are so small that they can often be jostled out of place as you remove your hands from the case when you finish your build. This can cause intermittent failures, and corruption of RAID arrays.
3. watch how you mount your fans so they blow air in the direction you want them to

Jam it back in, in the dark.