Or ...
1. attach ram to mobo CPU cooler may make RAM slots inaccessible
2. attach processor to mobo
3. attach cooler to processor + mobo attaching CPU cooler may require access to both sides of the mobo
4. attach mobo to case
5. attach hard drive to case can get in the way of mobo fitting
6. attach DVD drive to case can get in the way of mobo fitting
7. attach PSU to case can get in the way of mobo fitting
8. attach all power cables, case connections, DVD and HDD cables to their various places as tidily as possible
9. attach graphics card to mobo (and case) graphics card may make some motherboard connections inaccesasble
10. attach graphics card power cable