Michel Gagné is an animator who creates wonderful animated FX. Using a 2D style, Gagné has worked with Brad Bird on "Iron Giant" and "Ratatouille". It is worth researching his 2D effects channel on YouTube and then having a go at animating some of the FX.
Animated effects are often organically formed in the animator's imagination with a bit of planning but 'feeling' the animation by working straight ahead. Jason Lynch, our special guest stop motion feature film animator, spoke about this animation type and the animation principles in his recent workshop with SBIT animation students.
The other recently featured FX animator on this blog is Ryan Woodward.