Day hiked Mt Whitney twice (and have another solo permit for a day hike at the end of the month). There will be plenty of other hikers on the trail, even in the early morning hours, and in my experience everyone was social and friendly. I would say don't be afraid to chat with other hikers, ask questions, etc., and especially don't hesitate to ask for help if you need it.
As far as the nuts and bolts of the hike, it helped to study a topo map ahead of time, read descriptions of the trail, look at pics and videos of the trail, etc.; it helped me know what to expect and to keep me oriented.
If you start in the early a.m. you will be hiking in the dark; I would pay special attention right after Mirror Lake, it's easy to lose the trail there in some spots while hiking in the dark.
It helped me to spend a couple days at altitude before the hike; the first time I hung out at Onion Valley and the second time at Rock Creek.
It also really helped to stay hydrated before the hike and during the hike; I drank at least 4 liters of water a day for 2 or 3 days before the hike.
Anyway, have fun!
