I learn something every flight. I've done all of the above in terms of mistakes and have it drilled into my head not to get complacent. Probably the worst thing I've done is try and land on a short grass strip when I was sunburned, dehydrated and dog tired, but being the confident 'I can do that' type I overstretched myself. I managed it by the grace of God but gave myself a a good scare.
What I do is always put the GPS on, sometimes I switch it on and just leave it in it's case if it's a run I can do blindfolded. I download the log, run it on Google Earth and see how accurate my flying was.
The other thing I do is make each flight mean something, start collecting airfields or do some extra training in something that interests you. I have just over 100 hours and have a night qual, IMCR and about 20 airfields in the logbook. Don't just bore holes in the sky. If you look at one of the airshow sites there are always fly ins or air displays to go to. I plan these events several months in advance, so I have the a/c booked, the plates copied, any landing slots booked and the route planned way before I go. (I had the first slot booked at Duxford last weekend..
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So far I have 17 fly ins, interesting grass strips and museum visits planned up until September. In between that I do some instrument approaches and cct bash about once a month just to keep my hand in on flapless, ILS, NDB etc. Planning stuff works for me, I enjoy it for one thing, some folk might just like to turn up and thrash around which is fair enough but I think being proactive will keep your interest and your skill levels up.