After Tinkering with this achievement I finally figured out how to unlock it. You MUST buy 2 skills in the same category to make a list of skills. Let me Explain
If you buy 1 skill it will automatically equip. The achievement is to click on a skill yourself. You cannot click on a skill if it's already equipped thus taking away the achievement.
Now with 2 skills you will see one already equipped. Once you click the other skill and equip it the achievement will unlock as you just Equipped Yourself with a new skill...
See what I'm getting at? Clicking on a skill triggers the achievement. You cannot equip an already equipped skill.
So remember to buy 2 when you shop for skills.
The Ray skills Panzer Breaker and Deathphobia cost 3 jewels each. Thanks to AI Source!