I always try to pay for what’s in front of me and try to not speculate on rent increase etc. if I do manage to increase rents or pass expenses off to the tenants than that extra money is gravy. 

The guys that do that *usually* have decent paying day-jobs, and are more interested in having a bunch of paid-off properties for themselves or their kids when they retire than having an extra $150 per month right now. 

Condos for instance will charge HOA fees, limiting your net cash-flow.A PM will run 14-16%+ as they charge a month's rent to place a tenant, take an extra month to turn a unit and charge you premiums and overrides for the work.  

[So, can you see the result of adding all that extra income?]

Industry standards for most are earning the cash on cash return of 20% day 1, or within the first 30-60 days. 

With interest rates around 4% it's much better to keep the leverage on your home and use that extra money to earn a higher return elsewhere. 

But, for those readers who won’t go the extra mile to do a deeper search on techniques, here are a few off the top of my mind: Craigslist - They’re all over here, it’s like a piranha pond in my market.

I'm hoping to earn some extra income to supplement my day job.

Let's say one spouse works and earns money, and the other spouse doesn't work or earn any money.

Should I make extra payments on the mortgage, or invest it in the stock market.