Three common mistakes first-time homebuyers make are: 1) Not taking advantage of incentives like Ontario's First-Time Home Buyer Incentive which provides up to 10% off a mortgage; 2) Not managing existing debt which impacts mortgage approval; 3) Not budgeting for down payments and related fees, with less than 20% down requiring default insurance. Resources exist to help first-time buyers navigate the process successfully with careful financial planning and building trust with lenders.