What is/are the rule(s) for making this subjunctive?

What is/are the rule(s) for making this subjunctive?
 

Si te enfermes yo te lame un médico.

You need first the right conjugations here:
Si te enfermas, (yo) te llamaré un médico.

Notice that for this conditional sentence, you're using "enfermar" in the present and "llamar" in the future. Now try using the past subjunctive for the verb "enfermar", while you use the conditional for the verb "llamar". :)

How about this? Si te enfermaras, yo te llamarías un médico.

Very good!
Only "llamaría" instead of "llamarías", because "I" would be the one calling the doctor, not "you". ;)

Oh. Lo sabia. Gracias. Estaba en la luna.