You should buy a car before you desperately need one. This gives you time to research different makes and models, as well as allowing you to wait for incentive periods at the dealership. The internet may be an excellent resource for research.
If you are buying a new car, or a car from a dealership, it can be good to go car shopping around when the new models are coming into the dealership. The next year’s models often come into the dealership any time between August and November, and dealers will be trying to clear this year’s models.
On a regular basis, it can be best to head to the dealership on a day when you have a lot of time. The negotiations can take a lot of time, and you don’t want to feel rushed. A day in the middle of the week will be quieter at the dealership, and a salesperson may feel more pressure to get your sale because they have fewer customers available.
You may also want to head out to the dealership towards the end of the month. Dealers keep track of their monthly sales and often have monthly goals and targets. A salesperson may be willing to take less of a profit on a car in order to meet a certain target of sales.
You do not necessarily have to buy a car during a sale in order to get the sale price. If you go after the sale, you can still ask for the sale price.