I have a common 12V led strip (SMD5630) connected to my car battery directly. I have noticed that it gets really hot after a couple of minutes so I'd like to reduce the current it takes (now it's 1A) to get less heat, longer lifespan and less power consumption (of course in exchange of some brightness). How to do it properly?
The other solution that are mentioned do work but in my opinion the optimum solution to get the current/brightness that you want is to use a regulated 12 V (or less if you want) no matter the car battery voltage is.
You can get such a proper regulated 12 V by using a boost/buck converter module. They're not expensive and here's an example.
Note the screw on the blue potmeter, you can use that to get 12 V (or whatever voltage you need) at the output.
Did you measure the current of 1A? I would suggest to go for 1N54xx series diode to be on safer side.. It should work if the LED array is just passive..network of LEDs and resistors. Also, by default these diodes can withstand large pulses too expected from car battery.