Well shoot, even I can't find the post now.
Okay, on my car.... first thing, you need to make sure the "tang" from the intake gasket that sticks up between the intake and the head, is LEVEL or lower than the metal surface. If it's not, it pushes the gasket up and you get the dreaded corner leaks. It's also important to have your head and intake surface pretty even (as olddog stated). Mine were a good 1/8" off, but a cork gasket will compensate for that.
Now for the sealing... I use some quality RTV on all 4 points where the heads and intake meet. If you don't do this,
oil will leak there. For the gasket itself, I use the cork Fel-pro Printoseal gaskets. I am not a fan of rubber valve cover gaskets. First, I inspect the valve covers themselves, making sure the sealing lips are straight and level, and making any needed tweaks with a wide flat lip plier. Once straight, I use 3M super weatherstrip adhesive (comes in yellow and black) to seal the cork gasket to the cover. I let it tack, then put the gasket on, then place the cover on a flat table letting the weight hold the gasket in place. It also helps to put the bolts through the holes to also hold the gasket better.
Once adhered to the cover, I clean the head and intake surface with metal prep, and then install the covers, making sure not to overtorque them.
With this method, I have never had any pentroof I ever installed leak. The downside is if you need to replace the gasket, it's a tedious job getting it off the cover because of the 3M. But you can take the covers on and off a few times before the gasket won't squish down any more, so you might just have to change the gasket once a year.
Hope this helps.