Now I get about 1.5% their purchase price gross in rental income every month. After buying them and fixing them up the majority of the work I do on them is at tax time (still do taxes myself to stay in the loop). HOA and property management fees eat into it a bit, but it's not a bad haul. In addition to the cash flow, they've all appreciated from 20%-50% in the last couple years.
These days dividends from Apple stock (not bad for a tech company) and some other investments are doing better, though not even close to as well as the real estate.
The key is often to save up enough money to be able to take advantage of opportunities. For example, we just decided last week that we're moving to Florida. We were planning to rent, but we found a 3BR condo in a high-rise gated community on a golf course about 1mi from the beach for around $300,000 that went for $800,000 before the financial crisis. Luckily, we had the cash to be able to capitalize on the opportunity. I assume the property value will at least double in the next 5 years. Even if it doesn't, if we had to rent it out tomorrow we could break even on what we pay for the mortgage + HOA fees with rent.
It's risker than other endeavors, but investing in residential real estate like this is the best kind of investment I've found for my risk profile with the amount of money I'm willing to invest.
The hard part is getting together the initial capital to do so. I started working full time at 21 and it took me until around 25 to be able to make my first investment saving most of my modest income during that time.