Lessons Learned Journal - Best Practices

Hello altogether, I am looking for best practices / examples on how you document your lessons learned. Following the statement that "Good Decisions come from Experience which again comes from bad decisions" it is helpful to have a log of decisions,their circumstances and assumptions and for sure their outcome. Any good templates / format you are using, ways to log it, helpful information which should be decimented beside of the one mentioned before? @Mark and Michael: might be this would be a good podcast? So far I only know that I should do it and do it in a certain way, a tangible advice was missing so far for me. Thanks all, Christopher