what are those tweaks that help with performance?

I know in new vegas I used Ipreload size & I forgot what else

what values are the best & how exactly do I do this for skyrim?

Best is you leave the default values as they are. Better use the ENB Boost Mod (search for it on the Nexus, it should be File of the Month in August or at least in the top 5)

I really like using stakado enb & it is not compatible with enboost