@Ronaldo Carvalho I agree with @Brent Coombs that you need to know the cap rate in your area so that you can purchase above market.
Thou cap rates are important, you need find out what you want your return on investment to be. I generally use the 2% rule to determine a quick quant purchase price. This will give you a better idea of what your cash flow (profits) could look like if you were to purchase a property at that given price considering the associated expenses with servicing the debt and operating the property. Here's my general start to assess a deal.
1. Calculate what the Gross Operating Income is per month
2. Divide that number by 2%
3. The result is a purchase price that would yield a 24% annual cap rate.
3. Find out all cost associated with operating the property: debt coverage, management fees if your not going to self manage, taxes, maintenance, management, capital repairs funds,....etc.
4. Create a mock operating financial statement. :Income = gross months rent - 10% vacancy rate; Expenses = #3
5. Assess the numbers
6. Determine a offer price and if the property is a good deal.
There's so many other things to consider beside the cap rate but this will start you on the activity of assessing deals. Hope this helps! Message me if I can be of assistance!
DGBJR