1. Don't let skinny people plan your food. I was on the trail for 10 days when I met up with my buddies who were going to 'resupply' me. I ended up with 1 packet of oatmeal and a tiny slimjim for each breakfast, 2 total cups of trail mix (not per day, total!), stuff like tuna and saltines for lunch, and an average dinner of a mere 1 bowl of rice a roni for the next 5 days. If i had to guess I would say about 1200-1500 cal/day total for 12-18 miles/day. I spent my last $5 on snicker bars and was blessed with trail magic to keep from starvation or eating my skinny friend.
2. If its a debate on whether or not to bring that extra jacket, you should probably bring it. Its not that big of a deal to carry another 14 oz.
3. Thinlite + AT shelter = bad nights sleep
4. Don't start off too strong. Just because you have done 40 miles in a day before doesn't mean you can get off the couch and do 30 and be able to hike the next day (found this out for about the 5th time 3 days ago).
5. Don't try to hike 30 miles on 3 hours of sleep after a long week of school and work (found this out for the 3rd time 3 days ago).
6. Accept what gear you have, its weight, and which of it you will need for a trip. Just because a particular item is too heavy to 'justify' carrying (I.E. 5lb 0* bag, extra jacket, 2 quilts instead of 1) , but is necessary to keep you warm or safe, bring it anyway even if it means moving up to you're hauler pack. Don't be overly concerned with flashy basepack weight numbers or ego when you will still have a great warm time with an extra 4-5 lbs on your back and still 10 lbs less than youre struggling friends :)