"1. If it were to rain tomorrow, what will you do?" 'were' is past tense, and 'will' is future tense. It would be better if they matched, so, this would be better, "If it rains tomorrow, what will you do?" OR "If it were to rain tomorrow, what would you do?" 2 looks good! "3. This old man had 2 millions dollars, and he gave it to charities." This is good but for a number under ten, you should probably spell it out. So, "two million dollars." "4. He should eat lots of fruits and vegetables and drinks lots of water." The word "water" is plural, so drinks doesn't need the s. Just, "and drink lots of water." "5. He doesn’t know if should he bring a present when invited." There is a circumstance where this phrasing works: The boy knows he will be invited somewhere at a future date, but the invitation has not yet occurred. I doubt this is the situation you're talking about, though. It should probably be, "He didn't know if he should bring a present when invited." "6. If we had left earlier this morning, we wouldn’t miss the bus." Past and future tense mix up again. "If we had left earlier this morning, we wouldn't have missed the bus." 7 is a strange sentiment but grammatically fine, haha. "8. If I were you, I would talk to someone who look friendly" should be "looks friendly." 9 is perfect! "10. I can’t sleep with the night before taking a big exam." should be "I can't sleep on the night" or "can't sleep during the night." 11 is perfect, though it should end in a question mark. "12. Confident people dare to speak in the public." This does not need "the." 13 is perfect! "14. I really need it because of I have a math test" this needs a comma! And no 'of' "I really need it, because I have a math test." You could get rid of 'because,' too. 15 is great! "16. I am really anxious, because I can’t find out my backpack." 'Out' shouldn't be there. "Because I can't find my backpack." "17. Strange things are happened in our neighborhood." Tense mix up again! "Are happening" or "have happened" 18 is great! "19. Social situations aren’t bother you in the slightest." 'Aren't' should be 'don't' "20. Sometime you might annoy people because you’re so confident." Should be "sometimes you might." Also I noticed that you left off a lot of periods at the ends of your sentences, I assume you know about that already.

1. If it were to rain tomorrow, what will you do? -- Change order of these two. "What will you do if it were to rain tomorrow?" Notice that there isn't a comma in the corrected sentence. 2. I would give it to medicine research, if I got a lot of money. -- Change order of these two. It should be "If I got a lot of money, I would give it to medicine research." 3. "This old amn had 2 million dollar hat he gave to charities" sound more correct. 4. This is okay, I guess. 5. "He doesn't know if he should bring a present when invited..." This sentence is a little incomplete though, but that's just my opinion. It's not wrong saying this as far as I'm concerned. 6. This is okay. 7. I don't understand what you want to say in this sentence. It doesn't make sense. "If you don't know anyone, you could talk to Tom"? Maybe? I don't know. 8. Okay. 9. "......, I would take a long walk before I go to bed". Add the subject there. I just put in "I" because I assumed that was what you meant. 10. "I can't sleep AT night before taking a big exam." 11. "I don't have a gift. What if everyone else brings a gift?" 12. and 13. Okay. In 12 you don't necessarily need the "the" before "public", but it can be written with "the" too. 14. "I really need it because I have a math test". You don't need the "of" in "because of". 15. Okay. 16. Don't need the comma there. 17. Change "are" to "have". Are is present tense, but since you use "happened" which is past tense of "to happen", you have to use "have" in front of "happened". 18. Okay. 19. Change "aren't" to "doesn't" and take away the "in". 20. Add an "s" at the end of "sometime". Should be "sometimes". (^o^)v