Take my money
When the time comes to purchase your car and you have decided which make and model will be gracing your garage for the foreseeable future, you will need to work out your personal finances to arrive at what, is hoped, will be a sufficient amount to meet the monthly payment requirement.
Related: How much deposit should you put down on a car? (video)
A factor that is going to greatly influence your eventual monthly installment is the size of the deposit that you put down.
The question of how much is really simple, as much as you can! The general rule of thumb here is at least 10% but the more you can put down the better it will be for your eventual installment payment.