As DLoT said watch as many detailed PC build videos as you can and take your time and double or even triple check your work before powering up the newly built rig.
Using an anti-static wrist strap is always a good idea, it will ensure you don't zap any of your components with static electricity while handling them.
Make sure you have MB standoffs in the proper location on the case for your MB.
If the back of the MB touches the case at all it will short out which could damage it.
Do NOT over tighten the screws, snug by hand is all that is needed, if you over tighten them you can crack the PCB.
Also a magnetic tipped screw driver is an essential tool when building a PC.
One dropped/lost screw could easily short whatever component it is touching when the power is switched on.