Typically 75% of the rental income counts towards your income. 100% of the PITI payments count towards debt, when computing debt ratios.
Also, for conforming there is now a rule that you need to have 30% equity in your existing property (be it a rental or primary residence) before yuo can qualify for the next property.
Again, these are conforming rules. If you are getting a non-conforming loan some, none or all these may still apply.
