再也不做稀饭了-
回答你的问题：instead, instead of都可以放在句首，但是有条件的，请看语法：
instead意为“代替”“替代”，作副词用，通常位于句尾。如位于句首时常用逗号与后面阁开。instead 在顺接句子中作“代替”讲，而在转折（或逆转）句子中作“然而”讲。
例如：1.Lily isn"t here. Ask Lucy instead.
Lily不在这儿，去问Lucy吧. [注意]: 当instead在祈使句中时，只能位于句末。
2.she didn"t answer me, instead, she asked me another question.
她没有回答我，反而问了我另外一个问题。
二.instead of是介宾短语，其意与instead相同，不同之处在于它后面常接宾语，起宾语多由名词、代词、介词、短语、动词 + ing 形式充当。
例如：1.We"ll ask Li Mei instead of Mary.
我们将去问李梅而不问玛丽。
2.I"ll go instead of her.
我会替她去。
三.instead 与instead of的转换。
例如: 1.He didn"t answer me, instead, he asked me another
question → He asked me another question instead of answering me.
2.I"ll of instead of her.→She won"t go.I"ll go instead
instead的用法
instead是副词，意为“相反”、“代替”或“顶替”，常修饰动态动词，位于句首或句末。
If she cannot go, I can go with you instead. 如果她不能去，我可以替她与你一起去。
Instead, he asked his father why he was not able to hatch chickens while hens could. 他反而问他父亲，为什么他不能孵出小鸡，而母鸡却能孵出小鸡。
==========
instead of 用法归纳
ZZfrom http://61.146.93.114/Lydia/ReadNews.asp?NewsID=131
Some people seem to think that sports and games are unimportant things that people do, at times when they are not working, instead of going to the cinema, listening to the radio, or sleeping.
Instead of 的意思是“代替……”、“而不……”，其主动用法如下：
1． 作为短语介词，instead of 后面常跟名词、代词和动名词，偶尔也跟复合结构。例如：
I have come instead of my brother. He is ill.
I will go instead of you.
If I hadn"t got a cold I"d be working instead of lying here in bed.
Instead of doing it himself, he got a man to do it.
Instead of lending a hand, he laughed at us.他不仅没有帮我们一把，反而嘲笑我们。
They must make up their own minds instead of our making up their minds for them. 他们必须自己做出决定，而不是有我们来代替他们作决定。
It"s me that should ask you instead of you asking me. 应该是我问你而不是你问我。
2． Instead of 后面还可跟形容词、副词、动词、不定式、介词短语和从句，这时他相当于连词，但也有不少人认为他们是介词。但是，对中学生来说，重要的不是他的词性，而是他的用法。请看下面的例句：
Taking exercise every day makes him look younger instead of older. 每天锻炼身体使他显得更年轻而不是苍老。（连接形容词）
But the businessman grew worse instead of better. 但这位商人的情况没有好转，反而进一步恶化了。
I go to bed late instead of early.我总是很晚才睡。（连接副词）
That increased instead of decreased our courage. 这增加而不是减少了我们的勇气。（连接动词）
The price rises every day instead of sinks.
He proposes to do some work instead of to watch television.他提议做些工作而不是看电视。（连接不定式）
A word of encouragement might have made me respect instead of hate him.他若是说一句鼓励的话，那么我或许不会恨他，反而会敬重他。（连接不定式）
In warm weather he often reads under a tree instead of in the library.
天气暖和的时候，他常常是在树下而不是在图书馆里读书。（连接介词短语）
As a result, silver began to flow out of, instead of into, the country.
结果，银开始流出而不是流入该国。
3． Instead 单独使用的时候式副词，常用于句末。例如：
I"ve no coffee. Would you like tea instead.
我没有咖啡了，喝茶行吗？
It will take days by car, so let"s fly instead..
坐汽车得好几天时间，所以我们还是改乘飞机吧。
不过，用instead的句子也可以改成instead of：
She never studies. Instead, she plays tennis all day. → Instead of studying , she plays tennis all days. 她成天打网球，而不是学习。
He didn"t give John the money, but he gave it to me instead. → Instead of giving John the money, he gave it to me.
马老四-
如果你是中学生 不用他们那么复杂的讨论 考试只会考以下一个知识点：
instead 可以放句首，作副词。
instead of 只能在句中 ，原因是 of 是介词，后面必须带名词或代词。
赫赫 我也是中学过来的 知道这个知识点也是考点之一哦 加油哈~
慧慧-
INSTEAD OF可放在句首和句中 INSTEAD放在句末