There are dozens of great videos on YouTube that walk you through it step by step. Really if you can read and have a little common sense, things will be fine.
Build your computer on a hard surface like a kitchen table, you don't want static building up from carpet for example.
It takes a little more force than you would imagine to secure the CPU in place, don't be concerned.
Buy a pack of zip ties for cable management, and think about where you want the wires to go before you plug stuff in.
If adding more fans, make sure the airflow points in the right direction. A good rule of thumb is positive air pressure in your case (intake > exhaust), which helps keep dust out. Also, heat rises so you want your exhaust at the top and back and intake at the front and bottom.