If you think you are ready then that's great! There are plenty of good spells to pick from.
As for a spell that works, everybodies different, here's an example so a spell that worked for me may not work for you. A spell that worked for you may not work for me.
So pick a spell that interests you choose a catagory that catches your eye and look through the spell list.
For me it was banishing and protection spells, after I didn't see one that interest me, I wrote my own. Writing your own spells will be more powerful, just like casting one on your own is more powerful.