Take your time.
Do not overtighten screws holding the motherboard.
Take your time.
Do not slather on 5 pounds of heat sink compound on the CPU.
Take your time.
Do not force plugs. They are all keyed, but some will allow you to forcibly plug them in wrong.
Take your time.
Ground yourself and do not build it on carpet while shuffling your wool covered feet around!
Take your time.
Before touching ANY electronic component, touch some metal first to insure you are discharged.
Take your time.
Putting together the components is actually not hard. The software, on the other hand....
Oh, and take your time!
Disclaimer: If you chose to follow my advice, and you screw it up anyway,...it is YOUR fault. I will not assume any responsibility for your choices.