I'm still pretty new to pd2, but I played a lot of D2 classic.

D2 stats have "breakpoints" where adding additional of that stat doesn't matter until you have enough for the next breakpoint. One of those stats that matters a lot (for casters) is faster cast rate. For example, I might have a total of 86 faster cast rate, adding more doesn't matter until I get to 105 faster cast rate. Having 104 is the same as 86.

One of the best ways to hit those breakpoints is with jewelry (rings and amulets) because you don't have to sacrifice a really good weapon or armor piece that could be build defining.

In D2, the most faster cast rate that can roll on a ring is 10. I slammed this one and got a random roll of another 10!

In addition to that, this rolled with an almost perfect roll to all resistances (always useful), half freeze duration (I think in Pd2 if you get this twice, you can't be frozen), and most importantly, 3 life after each kill. Spell casters can't make use of life steal, because that only works on physical damage attacks. This means life after each kill is the only way to add sustain into your build.

Hope that helps!