What should a person know before assembling their first computer?
Solution 1:
Assuming you have all of the appropriate components and have taken the appropriate precautions to avoid static discharge, I think it is very important to install the CPU/heatsink and memory on the motherboard PRIOR to mounting the motherboard in the case. This gives you some freedom to operate, particularly on heatsinks which can be sort of a pain when installing. You can also use this opportunity to closely examine your motherboard and see where your auxiliary connectors for the case's power buttons/activity LEDs are going to go.
Speaking of heatsinks, make sure you watch a Youtube video for your particular model to make sure you're doing it correctly. The tabs can easily break off, be obstructed by a metal support frame under your motherboard, and whole bunch of other potential issues that could arise.
Once those are assembled, the rest is pretty easy/fun. Mount the motherboard, connect to the case's buttons and LEDs, then any PCI components, then get your SATA devices hooked up, and lastly, get your power supply in there and everything connected. I save the power supply for last because it can be a mess of cables and generally obstructive.
Once everything is done, grab the motherboard manual in case you get some boot tones and need a reference (usually memory that isn't seated correctly), boot up and enjoy a Windows 7 or Linux install sequence!
For drivers, I try to load as much on to a USB drive as possible, and I give them meaningful names (ATI Video Driver.exe instead of A1234907598.exe), and make sure I have ethernet/network drivers on there if needed. That way if a driver isn't working or isn't supported, I can hop on the net and download whatever I need.
Solution 2:
Speaking from experience, it's a pain to have to drop everything and run down to the hardware store for a tool you didn't think of. So, a checklist of necessary tools would be good to have. Offhand I can think of large and small flat-head and Phillips screwdrivers, non-magnetized of course; knife and/or scissors for opening things; antistatic strap and possibly an antistatic surface to put things on; perhaps narrow-nosed pliers or something for turning things in tight spaces; perhaps a small file in case of rough spots on a metal case; some cable ties to keep things neat. Probably missing some, haven't done it in ten years.
Solution 3:
Do NOT screw the motherboard directly to the case! Place standoffs in case, THEN put motherboard ON standoffs. I almost made this mistake on my first build.
ESD protection is something you need to consider. No sweaters or working on carpet. Buy a wrist strap or install the power supply in the case first, then plug the power supply in with the switch off (if your power supply does not have an on/off switch, buy one that does). Touch the power supply before diving into the case to discharge static.
Don't touch any circuit boards or PCB components, i.e. the motherboard, PCI cards, the PCB side of a hard drive, or RAM. Handle by edges.
Plastic "zip-ties" are nice for getting cables routed out of the way.
Also make sure you understand what all the jumpers do, make sure you've read and understood your motherboard manual. Try to download one if you don't have a physical copy.
Shake system a bit before the first power on to make sure you didn't drop any screws on the motherboard or anything else.