or start from simple skills that you can imagine... this is how i started!!
I 1st made suggestions of skills then got help from other maps etc.
I am not pro though on skills but IF you try do Sth and you try for much time and HARD then you can recognise the Other spells.! i have seen skills like Omnislash... leap.... and other skills in which powerful missiles are going through all directions!.. they are quite simple But it is quite impossible to make that kind of skills ... PErsonally i have worked on BLink !! and made two types.. the one teleports the Caster to the target and then an Illusion is Following the CAster like he moved Quickly ...The other skills that looks like BLink but it's not ! Makes the Caster Small ..Fast.. And give some special effects to feel like he is going really Fast !
And another one skill is NEW clear power...... Based on other skills...!!
You can do many things just from your imagination! This is going to take long though Dont stop trying!