Homebuyers can secure a mortgage interest rate below 6% by following three strategies. First, consider buying mortgage points, which can lower the rate but require an upfront fee. Second, an adjustable-rate mortgage with a 3/1 framework can offer a rate of 5.90% initially. Lastly, boosting your credit score is crucial, as the best rates are available to those with high scores. By combining these tactics and shopping around for lenders, buyers can improve their chances of obtaining a lower mortgage rate.