in加国家、城市、年份、月份、世纪、季节、颜色、风中雨中太阳下、树上。同时表示在......里面。还有in the morning、in the afternoon。记住这些就行了，不会考太难的。
on加具体日期、节日、星期、具体的某一天的早中晚，如 On a cold winter morning。on还解释为在......上面。一般考试只考on加具体日期。如on 27th May，1998.
at，只要记住两个：at noon、at night。就考这两个。
on 指具体的某一天，像寒冷的一天，暖和的一天等等，不要太纠结，想的简单点，不会超出考纲范围的。
1、时间介词 in, on, at
at < 天 (eg. noon, dawn, night, one’ clock)
on = 天 (Monday, 30th June, New Year’s Day, Mother’s Day）
in > 天 (2008, summer, April,还有早午晚)
注意：
1) 早午晚前后如有修饰语则用 “on”
On Monday morning
On a sunny afternoon
On the morning of May 23rd
On a dark night
2) on, in, at不用于下列时间之前：this, that, last, next, every, each, today, yesterday, tomorrow, tonight
3) in+一段时间可以表“…之后”
Eg: Hurry! The school bus will leave in five minutes
I will see my grandparents in a few days.
2、方位介词：
1）at和in
in 大地点 ≥town
at 小地点 < town
eg.: in town at bus station
in Beijing at school
in USA
2）on表示在物体表面上 eg: on the table , on the wall
注意：1) on the tree 长在树上 There is an apple on the tree.
in the tree 呆在树上 There is a bird in the tree.
2）on the wall 挂在墙上 There is a picture on the wall.
in the wall 嵌在强中 There is a window in the wall.
追问谢谢