Any advice from someone who has had a portfolio for 10/20/30+ years?

I've started my investing adventure 2,5 years ago. I've made a portfolio consisting of an all world etf and around 15 stocks. Growth, dividend, different sectors etc. So far i'm doing alright. And i'm looking to do this for the next 30 years as part of a pension (i'm a freelancer).

Although i know and talk to a couple of other people who are into stocks, i don't know any who are already in it for a longer time. Just like me they have only been doing this for a short time or they don't have a serious plan with their investments.

I was wondering if anyone can share some of their experiences or advice from all those years of building up a good amount of value by holding, trading or dcaing on the stock market. What did you learn? Did you change your strategy along the way? Are there things we should all know, things to avoid? What was your biggest mistake?

I'm hoping to learn more about it from actual experiences, instead of just reading the theories.

Thanks in advance!