Everyone says to keep it stock for a bit... But, that's not why I bought mine. I started modding my car as soon as I parked it in my driveway.
Anyway, I had to change a few things right away. My first mod was to unplug the relay that turns on one headlight at half power as the Day Time Running light. I feel that this was a STUPID way of adding a running light. So I deactivated it.
TINT - I tinted the windows in the first few days.
10" SUB - My car had the base stereo - adding a sub was a must.
LED interior lights. - I replaced all the interior lights with LED lights I made.
17x7.5 wheels - the stock wheels on my 13 were UGLY!
Lowered 1" on ProKit springs - I installed them myself. The wheel gap bothered me.
Then, my car was good to go for awhile...