Buy from Costco or Discount Tire — Both offer lifetime free rotation and balancing with purchase ($80–$120 value per set). Costco prices are typically the lowest for premium brands.
Don't cheap out on tires — The difference in wet braking distance between budget and premium tires can be 10–20 feet at 60mph. Tires are the only thing between your car and the road.
Buy all 4 at once for AWD vehicles — AWD and 4WD vehicles require all four tires to be the same size and within 4/32" tread depth of each other. Mismatched tires damage the transfer case ($1,000–$3,000 repair).
TireRack.com for research — TireRack has thousands of real owner reviews sorted by vehicle type. Even if you buy locally, use their data to pick the right tire model.