There are few do's and dont's based on my experience with SE phones.
1. Always, always backup your GDFS.
that way you will be safest before atempting any service operations. Use XS++
2. You must know the start address and length in hex when using the SEtool2 to perform the correct backup.
3. Always take care to bachup and note down the firmware version, fs version, customization (CDA) applied. Please note that it would be great incase one get all the information available in Service Mode on paper.
4. Start any service operation with full battery backup.
5. Remove the memory stick and sim module before attempting service operation.
6. Please arrange the firmware, fs and customization (atleast the generic one) before any service operation apart from GDFS backup.
7. Ensure the USB port is installed properly on your machine and the cable is the right model.
8. Take backup of your Phone data including contacts, SMS, custom templates, pictures, voice and recorded messages.
9. Keep a good service operation manual handy.
10. Try to keep some time inbetween subsequent service operations.
11. Keep a tab on battery status inbetween subsequent service operations.
12. Connect the cable properly.
13. After service operations let the phone safely boot donot press power on button repeated.
14. Please dont perform incase one has some ifs and doubts.
15. Flash operations require skill along with proper experience on chip flashing and flasher applications. Industry standard is Hi-Lo flashe with the propriety flashing applications.
16. Incase you are just attempting the firmware update/ upgrade operation, SEUS is one of your options.