Should = it's a good idea Must = it's a rule You should drive carefully in the snow. You must drive under 65 mph on this road. Sometimes must and should have the same meaning, but must is a little stronger. When you're in Italy, you should visit Rome. When you're in Italy, you must visit Rome. (same meaning but stronger)

"a lot more better" is wrong. good - better - best

Well, #2 is grammatically incorrect. You never use "to" after "should." A correct sentence would be: "I should get up at 6.00 tomorrow." The others are grammatically correct, but only #4 makes sense.

The volcano under yellowstone is HUGE and there have been lots of articles about what would happen if it erupted again. It would be a major disaster for all of the US and beyond. But there is almost no chance that this will happen today, next year, in 100 years, or even in 10,000 years.

If you add "yet" it means you think you will meet the person in the future. It is like 还没。。。呢 in Mandarin. I haven't met you = 我没认识过你 I haven't met you yet = 我还没认识你呢