常用的so句首倒装句有两种情况：一是so+助动词/be动词+主语；二是so+形容词/副词+主语+动词。
第一种情况的例句：
- So happy was she that she couldn't stop singing.
- So tired was he that he fell asleep right away.
- So pleased were they with the result that they celebrated all night.
第二种情况的例句：
- So loudly did he speak that everyone could hear him.
- So beautifully does she sing that it touches people's hearts.
- So quickly did they finish the task that they had time to relax.
使用so句首倒装句可以使句子语序更加紧凑，强调程度更高，为英语写作和口语表达增添了更多的表现力。但需要注意的是，so句首倒装句的使用应该恰如其分，过多的使用会使文章显得不自然。