なるべく質問は具体性のあるものにしてください。
たとえば分詞構文をまったく知らないのか，　ある程度は知っているのか，　なぜ分詞構文作り方を知らなくてはいけないのか（学校の教科書にあったとか問題集にあったとか），　分詞構文の問題でわからないのがあるとか。


（１）基本
従属節を分詞構文にする。　具体的には
１　接続詞＋主語　をとる。
２　接続詞＋主語を取ると残った動詞を現在分詞にする。　

As Tom felt sick, he stayed in bed for a while.
→　Feeling sick, Tom stayed in bed for a while.


従属節＋主節　ではなく　等位節＋等位節　の場合（つまり　and, but などでつながる場合）どちらが分詞構文になってもよい。

The train started at seven, and arrived there at nine.
→　The train started at seven, arriving there at nine.
→　Starting at seven, the train arrived there at nine.
（and の場合どちらかと言えば上が多い。）


（２）すでに現在分詞，過去分詞の場合はそれを利用する。
(つまり受動態の時は過去分詞で分詞構文を始めることができる）

When he was walking in the street, he met Alice.
→ Walking in the street, he met Alice.


If he was compared with his brother, he is much friendlier.
→ Compared with his brother, he is much friendlier.



（３）否定文のときは　not ＋分詞

As Tom didn't feel well, he stayed in bed for a while.
→　Not feeling well, he stayed in bed for a while.


（４）従属節の時制が，　主節より前なら　having + 過去分詞。
　　　完了形のときも同じ。

As he lived in Canada, he can speak English well.
→　Having lived in Canada, he can speak English well.


As I had seen him before, I could recognize him soon.
Having seen him before, I could recognize him soon.


（５）従属節の主語と主節の主語が異なる時は　主語＋分詞

As it was raining hard, I stayed home.
→　It raining hard, I stayed home.


参考：　（３）〜（５）がいっしょになった例。
As the train didn't come on time, he is angry now.
→　The train not having come on time, he is angry now.


（６）接続詞を残しても良い。
While he was studying, he was watching TV.
→　While studying, he was watching TV.


（７）従属節が　be動詞のときは being は省略してもよい。
As he is polular among girls, he is too self-conscious.
→　Popular among girls, he is too self-conscious.