1 如果强调 don't forget,你就应该使用either:
Dont forget,either,to have fun.-----------这里的either修饰don't forget
2 如果强调have fun,你就应该使用too:
Dont forget to have fun too.-----------这里的too修饰have fun.
又如:I didn't know that you had a sister too --------这里的too修饰 you had a sister .
I didn't know ,either ,that you had a sister---------这里的either修饰I didn't know.