一般现在时的用法
1) 经常性或习惯性的动作,常与表示频腮度的时间状语连用.
时间状语：every…,sometimes,at…,on Sunday
I leave home for school at 7 every morning.
2) 客观真理,客观存在,科学事实.
The earth moves around the sun.
Shanghai lies in the east of China.
3) 表示格言或警句中.
Pride goes before a fall.骄者必败.
注意：此用法如果出现在宾语从句中,即使主句是过去时,从句谓语也要用一般现在时.
例：Columbus proved that the earth is round..
4) 现在时刻的状态、能力、性格、个性.
I don't want so much.
Ann Wang writes good English but does not speak well.
比较：Now I put the sugar in the cup.
I am doing my homework now.
第一句用一般现在时,用于操作演示或指导说明的示范性动作,表示言行的瞬间动作.再如：Now watch me,I switch on the current and stand back.第二句中的now是进行时的标志,表示正在进行的动作的客观状况,所以后句用一般现在时.
////////////一般现在时表将来
1）下列动词：come,go,arrive,leave,start,begin,return的一般现在时表将来.这主要用来表示在时间上已确定或安排好的事情.
The train leaves at six tomorrow morning.
When does the bus star?It stars in ten minutes.
2）倒装句,表示动作正在进行,如：
Here comes the bus.= The bus is coming.
There goes the bell.= The bell is ringing.
3）在时间或条件句中.
When Bill comes (不是will come),ask him to wait for me.
I'll write to you as soon as I arrive there.
4）在动词hope,take care that,make sure that等后.
I hope they have a nice time next week.
Make sure that the windows are closed before you leave the room.