Hi @Ebrima Drammeh ,
A few general rules of thumb that I've found to be pretty true:
1) the famous 2% rule: See if the market rent for the property you buy is at least 2% of the purchase price. Ex) If you're looking at a house that costs $50k, you'd want the monthly rent you can command to be in the neighborhood of $1000. I think most people will say that it's difficult to find these 2% properties and I definitely agree.
2) the 50% rule: Whatever you're paying out in Principle, Interest, Taxes, and Insurance each month (so essentially your monthly mortgage payment), it should be 50% or less of what you're taking in each month in rent. Ex) If you're PITI payment is $400/mnth, you'll want a place that can be rented out for $800/mnth.
I have limited experience from just one long RE venture, but I found each of these rules to be pretty true (despite the fact that - when I first heard them - I thought they were ludicrous and ridiculously conservative).
Brian