1) First remove the faceplate by carefully pulling it towards you.

2) After that you have to remove the grey covers on the top and bottom.
Each of them has 6 clips which you do first have to loosen with the help of a thin screwdriver, a toothpick or something similar that fits through the holes.
Once a clip is loose you pull the cover up a bit to prevent it from snapping back in...
Some clips are pretty annoying, just move the cover around a bit until they finally get loose as well...











3) Then you will have to loosen the clips on the back of the 360 behind the ventilation holes. Hold the 360 like shown on the picture.
Then stick the 360 case-opening tool in each hole like shown on the pictures. Slightly pull the case apart to prevent the loosened clips from snapping back in once the tool is removed.





4) Once you are done with that loosen the remaining clips at the front then lift the upper part of the case up.




5) Now you have to make a choice. If you only want to flash your 360, replace the drive or the fan, then only unscrew what is circled in blue.
However, if you want to disassemble the 360 completely so that you only have the plain mainboard in the end unscrew everything (red and blue)


Only the ones circled in blue unscrewed

All unscrewed(red and blue)

6) Remove the eject-button and then lift the white case and store it in a safe place.



That's what it should look like (at least similar to this - there are a lot of different 360 revisions)

7) If only want to flash your drive then just unplug the SATA cable[[blue]. Unplug both cables if you are completely disassembling the 360.
Then carefully remove the DVD-drive by pulling it upwards.




8) Afterward remove the fan-shroud by pulling it upwards - there is a clip that fastens it in the fan.



9) Unplug the fan and carefully remove it as well by pulling it towards the middle of the mainboard and once it is past the metal overhang of the case, pull it upwards. There are two plastic pins on the underside of the fan so be careful not to tilt the fan too far before pulling it upwards, otherwise they may snap.







10) Now unclip the little white jewel attachment. Unscrew the three black screws holding the ROL board in place then unplug it by pulling it towards you.






11) If you unscrewed all screws(red and blue) before then you can now get the mainboard out of the case.
Do it like shown on the pictures, that is the easiest way.


12) Last but not least also unplug the last cables(SATA and power for the DVD).

Images by: Wilhelm 
From Xbox Experts