Not so good—Let me know if I can help.
不要说：如果需要我帮忙就说。

In many instances, the grieving person either doesn't know what help she needs or it's too hard to ask for help. Making specific suggestions and then asking her if it would be okay is much more concrete and useful.
在很多情况下，悲痛的人并不知道她需要什么帮助，或者对她而言寻求帮助很难。给一些具体的建议，问问她这样行不行，也许会更加实际有效。

Better—I think it's garbage day. Is it okay if I take your garbage out for you?
不如说：今天是扔垃圾的日子，我帮你把垃圾倒了吧？