Hello TheFly
I'm an English learner. If you don't mind, let me try to answer your question.
1. understand/understood...........ex. I could not make myself understand in English. (should be understood). why?
This one is a causative construct of a passive voice. I could not make {I (=myself) am understood in English}. "I am understood in English" means someone (like your friend) understands you when you speak in English. So "I could not make myself understand in English" means you couldn't speak English well enough to make other people understand you.
2. tried to/ tried +ing................both can be used. are there other verbs that follow this rule. what is the rule?
"Tried to do something" is used when you made an effort to do something but you failed to do it. "I tried to write a letter in English, but I couldn't". "Tried doing something" is used when you actually did the thing as a trial. "I tried writing to her to marry me, but she didn't reply".
3. may..........ex. may god bless you. i know it is a command but are there other examples that relate to this usage of a verb starting the sentence without an "implied you".
(EX-1) "May this moment be the worst of my life". (EX-2) "Long may she reign. May she defend our laws."
4.of vs. to............ex. he asked a very hard question of me. what is the rule with of.
"He asked a question of me" is the same as "He asked me a question". It is rather rare to be used in an active voice. But somehow its passive voice "The question was asked of me" is preferred to "The question was asked to me". This "of" is "out of (=from) a source"
I might be wrong. But you can be sure some of our moderator will come to correct me if I made any mistake.
paco