Here's how I do it:

Turn the Power Switch ON (Co-Pilot's side panel (Battery Power Panel))
Turn the External Power Switch ON (Co-Pilot's side panel (between the Engine 1+3 Generator Switches and the Engine 5+7 Generator Switches))
Pull all the throttle levers down all the way.
I always make sure that all the fuel feed switches are aligned so that there won't be a problem with fuel feed to all the engines (once you get familiar with the B-52 BUFF fuel feed, you can set them as desired).
[i]Simple way from here:
Turn all Engine Start Switches ON (Co-Pilot's side panel (Engine Start Control Panel))
Once all 8 engines reach ~20% RPM (on the Engine Tachometers on the centre Engine Panel (2nd row of gauges), (they will stop increasing once they reach this point anyway)), then press the F1 key, followed by a single tap of the F3 key. This should start all engines. Once started, press the F1 key again.
Turn all four Generator switches (Co-Pilot's side panel Engine 1 Generator/Engine 3 Generator/Engine 5 Generator/Engine 7 Generator Switches)) ON
Turn the External Power Switch OFF.

You should be good to go.

The difficult way is:
Start each pair of engines seperately by pressing the E key, then 1 key (for engines 1 & 2), followed by the Eng 1 & 2 Start Switches, press F1 once the 2 engines reach ~20% RPM, then tap the F3 key, and once the engines fire up, press the F1 key again.
Follow the above procedure for engines 3 & 4 (E key, then 2 key), engines 5 & 6 (E key, then 3 key), and engines 7 & 8 (E key, then 4 key).
To return to control of all throttle levers (in sync) press the E key, then the 5 key.


Note: I always make sure that all the fuel feed switches are open (aligned) so that there won't be a problem with fuel feed to all the engines (once you get familiar with the B-52 BUFF fuel feed, you can set them as desired).
By "aligned" I mean if the line runs like this -(|)-, make sure the swich is like this -(-)-. If is a (<) switch, make sure it's like this -(<)-.


Engin start video: https://www.youtube.com/watch?v=zu45XwRlzL0 (I uploaded it on April 11, 2011, so it's old). ;)

Although this video doesn't show a lot, it shows the pairs of engines be starting individually. You can also see the throttle lever movements used during the start procedure. You might need to watch it a few times to get the gist of what to do (I didn't have a microphone back then so there is no voiceover to help. Sorry).