Before starting the activity check the following :
1. Certification Matrix for Windows 2008 R2 (Based on your architecture 32 bit OR 64 bit)
2. Keep ready "Fallback Plan"
3. Keep ready Which method you are going to use (eg : Trasportable Tablespaces, Data Pump etc...)
4. Run CVU pre-upgrade check tool
5. Ensure consistent network setting
6. Mandatory/Recommended patches for upgrade