The best pvm necro build which I use every season to do Ubers with poor gear is
20 skeleton mastery
20 corpse explosion
20 amplify damage
1 clay golem
1 golem mastery
1 summon resists
Rest of points in revives
When switching to doing ubers I revert to only 1 point in amp and like 10/10/10 clay golem 10 golem mastery and 10 revives
That is because the higher clay golem slows combined with decrepify is very important with lesser gear.
Later with godly gear I switch to 1 point in iron golem and 20 in mastery to make the iron golem into a pride conc aura
But the 3 most important part is skeleton, Skeleton mastery and corpse explosion.
Never use skeleton mages, they are weak and do weak damage that isn’t amplified by auras except infinity