Hi Sam
Scott writes a very good book on updating pcs - he starts building at 25mins
https://www.youtube.com/watch?v=dw3mcaWihBI
Top tips:
Is there a PC pro who can help.
Read the motherboard instructions they are your friend
I suggest you read everything, your case manual, cooler, power supply, gfx card etc
You need a well-lit table top, with a few towels/sheets and newspapers so you can lay your case over and set your stuff out safely
Desk lamp and torch may help
You often just need a medium Phillips screwdriver - don't drop it into your motherboard
Don't moonwalk around in nylon pants and touch your pc innards
Do use the motherboard standoffs (usually brass threaded nuts which fit between your case and your motherboard.
Scotts case has a removable motherboard panel which makes fitting stuff easier
Some Pros advocate building it outside the case to see it works
Having a wired keyboard and mouse can make set up easier to start with
So you know which slots to fit your memory?
Which slots to fit your optial drive? SSD? HDD?
Read about the case cables and where they fit into the power led, hdd activity light, reset, power on etc
Read about the Bios set up in your motherboard manual
Be careful with the CPU socket and your CPU pins and don't bend them
Squeeze out silver paste away from the MB and lift it over with a slice of credit card or similar
Have a hosepipe and fire extinguisher handy, joking.
Take some pics and post it on here in the project section - good luck.