Is there a general rule for changing verbs into nouns?
Is there a general rule for changing verbs into nouns using miento? For example: to suffer (sufrir) into suffering (sufrimiento). Herir (to wound) into herimiento (the wound).
I don´t think there is a general rule. Rather, there are many possibilities, just like we have in English. Many verbs that come from Latin can use "ción", like "invitar - invitación". Others, like you say, use "miento" or "mento". Verbs ending in "ear" often use "eo" like "cosquillear - cosquilleo".
If you are interested, you might enjoy the book "Guide to Spanish Suffixes"