What I would do differently:
Landlording: Wait a little longer to find a better tenant. Don't just go with the first candidate, stick to your qualification standards. Be strong! I almost got sucked in with the first prospective tenant, with an eviction on their record. They wasted some time, but thankfully I refunded their partial deposit before they moved in, then stuck it out for another month to find the best tenant. Oh yeah... and don't accept partial deposits, just the full amount :) .
Buying: Ask seller for more before closing - ie, CLUE report to see any past insurance claims that could increase your premiums. I would justify a lower offer/price with reason, in writing. I would have included repairing the droopy ceiling, fixing the cat pee stench etc. Use bigger pockets report tool (from the calculators) to showcase repair items and to back up your offer with reason. I didn't do any of these things, and I could have gotten a better deal.
Selling: My first property was a condo in Melbourne, Australia. It was in a great spot, and I sold it before I got into investing, darn it! I hired an agent just before moving back to the US. First off, I should have kept it, because Australian real estate went crazy over the past 13 years and the building had a bunch of serviced apartments through a leasing company I could have worked with. Secondly, I should have vetted the agent better. After 6 months, the property hadn't sold. So, I made a surprise visit back, and it looked like he had been living there (dirty bathrooms etc). I fired him, got another agent and sold the place within 2 weeks with a reasonable profit!
However, I will take those lessons and more to the next deal. I'm not going to do everything right, especially the first time, but I'm going to keep doing real estate investments, and overcoming my fears. The most empowering thing I did was to accept that I'm going to make mistakes, learn from them when they happen, and know that I'll do better next time - and never ever give up!