One crochet technique that I picked up several years ago (and which I now couldn't live without), is that of work a stitch (or stitches) into the back bar of the foundation chain.
To my mind it is a much overlooked and under utilized tool that every crocheter should have in her (or his) tool kit.
The first thing a crocheter needs to pay attention to is the fact that a chain has both a front and back. Here is a photo which I think shows the difference between the front and the back -- the top chain shows the front, while the bottom chain shows the back:
This next photo shows a detail of the "back bar" with a yarn needle inserted where you would insert a hook if you were going to crochet a stitch:
And in this photo, I've replaced the yarn needle with a hook:
and here I've zoomed in so there is no question about where the hook should be inserted:
From there, a crocheter can go on her (or his) merry way and complete the stitch. Here I have worked a single crochet:
This technique can be used in a number of situations, but is particularly useful when making amigurumi and any time you want a tidy edge for easier joining.
I've also heard that when you work the foundation chain of Tunisian crochet through this "back bar" it helps reduce curling.
I don't know that this tip will transform your crochet life as much as it did mine, but I hope you find it useful.