首先,让我们来了解一下"than"这个词的特性.
than在两个物体比较的时候,前后两个物体必须是同一类的东西.比如猫和猫比,狗和狗比,人和人比.当然,你要说 A cat is shorter than a man.就错了,虽然猫是肯定比人矮的,但没人会这么去比,这么去说的,对吧.你可以说 My cat is fatter than yours.就对了.
than前后除了要接同一类别的东西外,词性、时态也得一致（当然也有例外,比如说我今年比去年高是： I am taller this year than I last year was.）
再举个例子：“比起篮球,我更喜欢足球.”你可以说
I like football better than basketball. √
I like to play football better than to play basketball. √
I like playing football better than playing basketball. √
I like playing football better than to play basketball. ×
I like to play football better than playing basketball. ×
反正记住一点,than前后要对等.
好,现在来看看上面那两个句子.
第一句There is no better way than to help others.这句话严格来说不是很对.其实其完整的句型是there's no better way to ...than to.例如：
There is no better way to rest than to listen to music.
没有比听音乐更好的休息办法了.
There's no better way to save that boy than to do a surgery on him in time.
为了救那个男孩,没有什么方法比及时为他做手术更好的了.
所以现在明白为什么第一句话后面是to do了吧?
至于第二句There is nothing more useful than having a good friend.就一目了然了吧.这句话比较的是对象是nothing和having a good friend.名词和名词才能相互比较,nothing是名词,having a good time是名词短语.having既是have的ing形式也是动名词,这个你们应该学了的吧.
所以现在明白了吧.
记得给我加分啊.天天向上!