So I'm going to be hooking up my HIDs with a relay and everything but what would the best way to connect it to the battery be... and also where should I ground it?

 

If you check on ebay, they sell HID kit it all plug and play so u don’t have to worry about those stuff. BTW make sure you get the one with high and low beam. Let me know if you have more questions.
And about were to ground it i can send you a pic of where i ground mine so you can get some idea. Just let me know.