As long as you take proper ESD precautions and research your parts compatability properly it's safer than it's ever been.
Motherboard choice will be dependent on CPU choice.
RAM is easy - DDR3 is pretty much the only standard in use ATM (mid 2012), DDR2 is considered legacy and DDR4 isn't ready yet - higher numbers are compatible with lower requirements. High end systems (Sandy Bridge-E at this point in time) use a Quad Channel RAM configuration which means you need multiples of 4 sticks of Matched RAM. Mid to High end (most of what an enthusiast would WANT to build) uses DUAL Channel, i.e. multiples of 2 sticks of matched RAM. And low end setups still use single channel, so you you can mix and match brands and capacities across the board.
Pretty much all Graphics cards are PCI express now however just make sure you have adequate PSU power. Here spending more really does make a difference. A name brand 400W such as Corsair is miles better than a no-name brand "800W" (hint the 800W isn't).
Beyond that just be patient, research component compatibility (if in doubt ask) and you should be fine.