Housing affordability guidelines include the 30% rule, suggesting no more than 30% of monthly income on housing costs; the 28/36 rule, recommending no more than 28% on mortgage and 36% on total debt; and the 3X annual income rule, advising a mortgage no larger than three times yearly income. Factors affecting payments include mortgage rates, private mortgage insurance, property taxes, insurance, and lender terms. Lower rates can be achieved by improving credit and down payments.