Haven't notice dead spots excepts when my guitar needed adjustments. It needed intonation.
First you got to choose the string gauge you like.. And get a pack of brand new ones..
Then you set the neck relief the way you want it... If you like it, don't play with the neck! Just make sure the strings aren't too close to the neck. A reasonable relief allows the sting to vibrate completely with a lot of overtones...
For the intonation, tune your new guitar strings (with an electronic tuner)...
Strings that are smaller then 10-46s sound thin on a SG and chosing them makes it easier to "get" dead spots...
Then make sure the harmonics at the 12th fret of each string sounds in tune. It has to be dead on!
Now that your guitar seems tuned, the next step is to fret each string at the 12th and again, check if it is in tune. Depending on how the pitch is on a string, adjust the saddle that goes with it.
It sounds a bit too high? ( If you don't hear it but see the tuner indicates it's slighly higher...) Bring back the saddle.
Sounds too low? Screw it closer to the neck.
You got to make sure it sounds dead on in all 3 ways: open, harmonic 12th fret and fretted 12th fret.
Tune your guitar again. It should sound allright. Without dead spots... Of course, even with absolutely incredible guitars, you do get spots that don't sound as rich as others.
If you still have the dead spots' problem, I'd say bring it to a luthier.
If everything's allright, play...
