Always use a checklist and check it twice-It's only happened a few times but occasionally you forget something (Bear bag string, toilet paper, knife and spork) but when it does it's darn inconvenient!
Hike your own hike-Everyone hikes at their own pace and should indeed do just this. The biggest group I have ever backpacked with was 5 and 1 dog. Everybody has a different idea of how fast to go, what time to get up, what time to go to bed....how many pics to take etc etc The best thing you can do is accept everyone elses point of view as valid and accept it. Don't expect anything else. Having said that I have come to believe it is important to find a hiking partner(s) who think similar to yourself. When I have been fortunate enough to do just that those trips have been the most rewarding.
Be extra careful toward the end of a hike when you are tired. I have been lucky so far but I can tell you that I am much more prone to accidents when my feet get heavy. When you get tired, slow down, get very deliberate. Place each step carefully. Make conservative decisions.
Don't take short cuts. I can think of at least two examples where I got my boots wet trying to avoid stopping to put on my water sandals....the ones I purposefully brought for such occasions. I almost got injured in both situations. Stop.....take the pack off...put the sandals on....take your time.......better safe than sorry in the back country...oh and both times I was solo.
Never separate from hiking partners that don't know the trail. I have only been afraid twice on the trail and both times it was as a result of separating from my partners....once at Keji in the pitch black and once at Cape Chignecto. I will never forget the pit in my stomach during the times that I thought they were lost. Patience is a virtue.