1) 误:Only this, we can hope to do the work well.
正:Only in this way can we hope to do the work well.
2) 误:It was dark, they had to feel their way upstairs.
正:It was dark, so they had to feel their way upstairs.
It was so dark that they had to feel their way upstairs.
It was dark; they had to feel their way upstairs.
As it was dark, they had to feel their way.
例1)里的"only this"在整个句子里不合乎语法,纯属中国式的英语,而且本句以"only"开头,要用倒装语序。例2)也是按汉语的习惯,两个单句之间不用连词,直接用逗号隔开;而英语则要么有连语;要么用分号或句号隔开。