How to select external components for LM2596-3.3V?
For a given step-down chip, component values depend on what the input and output voltages are, and how much load current there will be. You can use the datasheet to figure out best components for your requirements of 12V in, 3.3V out and whatever your maximum current is, but this chip can only go up to 3A.

One thing to watch out is how much you can tolerate output voltage ripple before the powered chips stop working properly, but often there is no supply voltage ripple tolerance specification for chips. Too small output capacitor with high ESR can lead to ripple that is too much (tens if not hundreds of millivolts), and larger than necessary capacitors with low ESR might get ripple down to millivolts which could be far below what is necessary for the application. Basically the rule is, put only the amount of capacitance you really need.

Another thing to watch out is the voltage swing that happens when load current suddenly changes. A processor might be in sleep mode consuming 1mA current, and suddenly it wakes up and takes 100mA gulp of current. These sudden load steps can cause the voltage to sag momentarily, so the output capacitor needs to have large enough capacitance with small enough ESR to handle this.

Other caveat is that different capacitor types have different ESR characteristics. Low ESR is better, but paralleling few ceramic capacitors can result in extremely low ESR which the switch mode regulator chip can't handle well and it won't work properly.

Ceramic capacitors also lose capacitance under voltage bias, so a 100uF 16V capacitor can have 100uF capacitance when it is discharged to 0V, but it might have 50uF of capacitance when it is charged to 16V, so that would not be enough if 100uF capacitance is needed.

I bet there are many more reasons why you have encountered differently designed LM2596 designs than the ones I already listed.