Always negotiate before getting in. While general ranges exist (40-200+ baht depending on distance), research specific fair rates for your destination since prices vary significantly by route. First quote is usually double the fair price

Show them the destination on your phone map and agree on price clearly. Some drivers will try the 'meter broken' or 'special price for tourist' routine. Grab taxis are often cheaper and less hassle, but tuk-tuks are fun for the experience once or twice