Many years ago, I settled on using "HiTack" spray... a coat on the gasket
and a coat on the gasket rail of the valve cover.... let them "tack" and
assemble... A small dab of silicone where the intake manifold and cylinder
head gasket rails meet will help immensely.

Torque the covers carefully to avoid belling the material around the bolts
(indeeed, make sure they are straight and flat to begin with) and make sure
you are using those little plates under the bolt heads to spread the
clamping force. If you are using the cork gaskets, be aware that they can
shrink over time and usually require occasional retorquing until you no
longer "gain" on the bolts.

FWIW, intake manifolds and valve covers are two areas I like to repeat final
torque sequence on several times once I have achieved target torque...