So what I do when I look at a property is this-
Find the property I am interested in- If this is a "normal" rental (not low income/section 8) I try to find a home with some built in equity (who doesn't?!)
I then look at the area and see if there are similar homes for rent in that neighborhood. I use zillow/call rental signs/ craigslist or call my realtor.
I then calculate the mortgage, taxes, and insurance costs
Factor in repair costs.
Ananlyze the data and determine the rental amount based off comparables. A lot of factors come into how much you should rent your house out for. The question I always ask myself (with anything I pay money for) what is the benefit I get for spending that extra dollar? For a person who wants to rent your house, this may be a question they ask themselves, so why would they rent your home over the others in the area? What is your advantage and what are you willing to accept for that advantage?
So an example would be something like this:
House size - 2400 sqft 4bd/2ba
Cost - $160,000 (Assuming Closing costs rolled into loan)
Taxes- $3200/yr
Insurance - $800/yr
20%down @ 30 years w/4.5% interest rate - PITI = ~ $1144.00
Comparables are between 1300-1500 for home with similar size and location
I would look at this and say sweet I could net $356 a month if I'm at the high end of the rental market! But am I? At that point you have to factor in your advantages. Is the home in a "better location" than the other homes, does it have upgrades in it that would make it more appealing or warrant higher paying renters? What kind of market are you appealing to is really what you're looking to answer. At that point, you can make your decision and based on what you decide can determine if it is something you want to get into. Is making 200$ a month cash flow worth it? Maybe.. maybe not. Does it come close to the 2% rule? It's tough to come to a conclusion and you need to be wary of analysis paralysis. Inaction can kill ya.
I would suggest reading up on some more information on this site and maybe some books to see what other options you may have. There's a ton of great info out there! That being said I'll leave this link right here for you to check out if you'd like.
http://www.biggerpockets.com/renewsblog/2010/06/30/introduction-to-real-estate-analysis-investing/
I wish you the best of luck and if you have more questions... ask them!!
-Drew