Should help you commit those spells to memory faster than just trying to remember them in-game.

http://www.reddit.com/r/DotA2/comments/sqb9r/invoker_trainer/

tis good but thats only like 10% of playing kael

Its the first step though.

I don't usually ever play Invoker because I tend to get flustered when shit goes down. However, I saw a video where Purge practices with him in -wtf mode (no cooldowns). It seems like a good way to get an idea of how spells actually work (delays and such) as well as quickly memorizing them.

http://www.youtube.com/watch?v=oef8BmFrI0w

The Invoker playstyle reminds me of the game Magicka - except in Magicka you have 8 elements as opposed to 3. It's a seriously underrated game.

The level of frustration when trying to think on your feet and put together appropriate spells is exactly the same.