Quote Originally Posted by Misha Tal View Post
Hello all!
Often when a word is preceded by the prepositions "с" and "в" (and sometimes also other prepositions like "от", "над", etc), it's possible to add an "о" to the preposition to make the pronunciation easier:
в всяком случае --> во всяком случае
над мной --> надо мной
My question is: when is this allowed? Is there a general rule? Are there set phrases? Or just any time you feel like the consonants are really stepping on each others' toes?
I mean, I can say things like "с встречей", but if an "о" was allowed, I'd really appreciate it!
Thanks in advance.
Well, if i understand you clearly...

со встречей = с встречей, оба варианта правильны, можно вставлять "о" для благозвучия перед словом начинающимся на некоторые согласные, но не всегда можно и не всегда обязательно, например "с женитьбой" only, но "со свадьбой" and it doesn't depend on letter "с", so "с сестрой", but not "со сестрой". Возможно что "со" ставится когда слово с 2 и более согласных начинается.

гораздо проще с о/об: "о книге", "об авторе"
AFAIK english speakers pronunce "r" in word "or" when next word is started by гласная.