My biggest property investing lesson: know your cash flow. It doesn’t matter if the property is positive or negative cash flow, but you must know what it is before you buy to make sure it matches your personal circumstances.
When we bought our first three properties we had no idea what the cash flow was – we just knew buying investment properties was a good idea. Then we ran out of money! Our spare cash flow dried up until we got a tax refund and were flush with funds again. We smartened up after that and always ran the figures before investing. But in the last 10 years of consulting with clients I have met too many people in financial difficulty because they didn’t calculate the cash flow before investing.