I always forget about the kill ring, or rather I used to. I’ve made a habit of using it lately. Its just so damn handy, I don’t know why I could never grasp it before. For those who don’t know, anytime you copy or “kill” text in an emacs buffer, its get placed on the kill ring. This includes certain basic functions like kill-word. So, often, I would copy some text I wanted to use to replace some other text (we’ll say a word, for example), then kill the word I want to replace. This would mean that when I yanked the text (ctrl-y, basically emacs’ paste), it would insert the last thing killed: the word I want to replace.
However, the copied text is still accessible on the kill ring. After the initial ctrl-y, meta-y will cycle through the kill ring’s other (previous) selections. Its sort of difficult to describe; just give it a shot! It’s become a huge time-saver for me.