how to follow up mails in gmail

Sometimes its necessary to follow-up a particular email;and after sending it,we realise that we forget to take steps to do so.
The easiest way will be to organise the mail before sending it.
Gmail added this feature of starring or labeling  them before sending.
From their blog--

When composing a new message, you can assign labels or star it by using the labels drop-down menu. As you’d expect, recipients of messages organized this way won’t see your labels or stars.