Ioannis Anastassakis has a great book called "The Art of Rasgueado". There are a lot of different rasgueados and you don't have to use all of them. The traditional p-a-i triplet and sextuplet rasgueado, the e-a-m-i-i rasgueado, and the a-m-i-i rasgueado are probably good ones to start with. The a-m-i-i is an ornamental rasgueado, the other two are for longer passages, the p-a-i commonly referred to as the "continuous roll" rasgueado.
A bit about execution: You only want your nails to skim the tops of the strings, don't drive them into the strings hard. You get a much better sound and it will allow you to do them faster. Also, some videos on the internet recommend you anchor your thumb on the 6th string. Do that if you don't need the low E string for a note. If you do, anchor it just behind the string, it'll feel weird, but that's how the true gypsies do it. That's for the a-m-i-i and the e-a-m-i-i. For the continuous roll, the motion is that of opening a doorknob. Practice it very slow at first and let the motion become second nature, and don't move your hand away from the strings too much, what it is is an upstroke with the thumbnail, then a downstroke with the a finger and another downstroke with the i finger. Challenging movement, but if you practice, you'll get it.
Now when you're ready I'll tell you how to get some lightning fast picado.