DoT SP efficiency?

[HungarianRhapsody]

.... I didn't know you could stack the same dot more than once...

That makes a big difference!

Any other tips like that I might have missed?

Niacs/Eldars stack for up to 3x damage. As long as you keep the stack going, it will remain at 3x damage.

Black Dragon Bolt does not stack for multiples on itself. Black Dragon Bolt kind of sucks unless you are fighting something that is vulnerable to Acid, immune to Cold + Electric and you have a healthy amount of Acid enhancements. And even then, it's not spectacular.

[Matuse]

.... I didn't know you could stack the same dot more than once...

That makes a big difference!

Any other tips like that I might have missed?

Yes. Read spell descriptions. For every spell.

DoT self-stacking is explicitly described in the spell's tooltip.