Compared to some on here I am a novice but I have been buying and renting properties in smaller numbers for 7 years.

-Buy low and sell high or hold

-Flipping is 100% about the cost to buy and repair against the opportunity to sell at a higher price- I have little exp. here

-Renting is long term wealth building and it is most effective if the income is reinvested in new rental real estate rather than lived on

-The longer the you hold and rent a property the better the return seems to get because you know it and anticipate its problems, rents tend to go up with inflation and you can refinance at lower payments as the equity is more.

-Tenant management is often as important as the property so a good property manager who is good at both is vital to success.

-It is not a passive investment though it can be mostly passive.

-Get good liability insurance on every property

-Location- Location is of prime importance but depends entirely on what you are trying to do with the property. The most important thing is to understand the dynamics and demographic shifts of the neighborhood, city etc etc. Its not enough to just go see the property if you are buying in an area you don't know well. You should grasp all the dynamics of the area- good schools, universities, amenities, hospitals, crime rates, social economics in the area, distance from where jobs are at in the area. That doesn't mean you need to buy in the nicest areas but you need to know what the draw to your property will be for you tenants.

-Have a adequate cash reserve for anything that could go wrong, and things will go wrong

-Rents generally need to cover 10-20% for management, the cost of the mortgage, 30-40% for maintenance and repairs and still cash flow. That's not always easy to do so the deal needs to be right.

-Grow a thicker financial skin- I actually think this is one of the most important parts and a big part of this is simply experience and the number of properties you have. The more experience you have and the more properties own the more you will run into uncomfortable situations and unanticipated costly repairs. The first time you get a bill for the cost of a new furnace or something similar it feels crippling to the investment. The earlier that happens the more you will second guess the entire decision. Running into enough of those situations over time helps you realize that you planned for that contingency and it won't break you if you started out with a solid plan.

-The better the cash flow and the more sources of cash flow you have the more real estate investment gets powerful- This is kind of a continuation of the above thought. The more properties you own the more frequently financial pressured decisions manifest but you also have several sources of cash flow that cover the impact of the costs from expenses in the short term. Example: Monthly rental income totaling $600 including the amount you expected for repairs, if coming from one property means that a $4000 furnace replacement will take you over half a year to recover. It becomes difficult to see a successful year even if you have cash reserves. Now consider that same scenario but with 10 properties where monthly rental income totals $6000. That cost doesn't even take a whole month's generated income. Generally the larger costs are infrequent and that means that larger the cash flow the less costs impact your decisions and the more you can reinvest the income in new rentals.

-Having experienced mentors in any kind of real estate venture is invaluable. They can give you huge clues and talk you off cliffs.