Which car battery terminal to connect first?

When removing the old battery, remember to first disconnect the cables from the negative terminal, which is usually black and has a minus (-) sign then disconnect the cables from the positive terminal, which is usually red and has a plus (+) sign. Take caution at all times to never touch a metal object to both terminals of the battery at once. 

After disconnecting the terminals, unhatch the clamps securing the battery in place and slowly lift it out of the battery tray.

Before placing the new battery in position, ensure that both terminals and the cables are rust-free. If they are rusty, you can clean them with water, baking soda, and a wire brush. 

Next, lower the battery onto the battery tray with the terminals in the right position, and clamp it into place. Now connect the new battery in the reverse order, connecting the positive terminal first then the negative. Make sure that the battery is secured in place!