1、就我所知道的以下一些情况要加ing：
①作主语时要加ing.看句子里有没谓语动词,如果有,则该动词就要加ing构成动名词作为句子的主语.如：Walking in the street,she saw an old friend.
②表示伴随、原因等状语的时候要加ing.
③句子为现在进行时,要加ing构成现在分词,用来修饰名词,作定语成分,表示某动作正在进行.例：We are waiting for you now.
④作宾补时要加ing.在某些感官动词如see,watch,notice,hear,feel,find等和某些使役动词如keep,leave等后可用V-ing形式作宾语补足语.例：He saw lucy walking after supper.
I'm sorry to keep you waiting.
⑤作主补要加ing.如：He was said going abroad.
⑥有些介词后面要加动名词,如for、of、with等.例：She is looking forward to seeing him.
⑦V-ing形式的固定搭配时,如have difficulty (in) doing sth.或者feel like doing sth.等等
例：I don't feel like eating anything at the moment.
⑧动词并列时要加ing.例：She stood here,reading a book.
判断祈使句：句子开头以不加ing的动词所引导的句子就是祈使句,因为句中没有谓语动词,该动词要充当谓语,故不能加ing.例如：
Go down the street!或者 Give me the glass please.
注：以动词+ing或ed为句子开头,一般是非谓语动词的用法,表状态或其他；而以动词原形开头,一般是在祈使句使用.
2、funny是形容词,而fun可作名称、动词、形容词.看在句子中充当什么成分再选择.
3、other表示另外的,其他的,修饰复数名词.例：What other animals do you like?
another 表示三个或三个以上的又一个、另一个,用来代替或修饰单数可数名词.例：I don't like this one,please give me another.
the other一般用来表示两者中的“另一个”,经常与one搭配.例：She has two daughters.One is a teacher,the other is a doctor.
4、rain：作名词时,译为“雨”；作动词时,译为“下雨”.
rains：表动词第三人称单数.eg.It rains.表示一个地区常常下雨,用来形容一个地方气候多雨.
raining：动词现在进行时,表示动作正在进行.eg.It's raining.正在下雨.
5、maybe是副词,“也许、可能”,在句中作状语,相当于perhaps,通常位于句首.而may be 是情态动词,相当于may+ be,may是情态动词,be是动词原形,两者构成完整的谓语形式,与主语形成系表结构,意为“也许是、可能是”.如：Maybe you are right.= You may be right.
6、on vacation指正在度假,而take a vacation与for vacation都可译为去度假,本质上没多大区别.
7、tour多表示短途的旅行,而travel则一般表示长时间、长途旅行.tour在句中主要用作名词,而travel可以用作动词、名词.
8、necessary和important主要是意思上的区别,necessary表示必要的,而important表重要的.
9、all 用于冠词、所有格或限定词之前,而whole用于冠词或所有格代词之后.例：All the vacationers enjoyed themselves.
He ate the whole loaf.
简单的说all=the whole.如：All the winter passed uneventfully.=The whole winter passed uneventfully.
但whole若与a连用时,不可用all代替.如：I waited for her a whole half hour.
另外注意,all与复数名词连用时,后面常不带the；whole若与复数名词连用时,前面一般不加the.例：All workers joined the general strike.
Whole Indian tribes were killed off.
希望可以帮到你.