Crochet Tips: Increasing and Decreasing

What does my pattern mean when it says 'Increase'? I remember being flumaxed by patterns that just said 'inc'. I've found this most often in Amigurumi. Some pattern writers will say 'DC x 6, 2Dc in next stitch', while others will write 'DC 6, inc'.
Some patterns will give you information in the pattern notes about exactly what they mean by Increase or Decrease.
If there is no information then you should assume that for increase you place two stitches in the next stitch and for decrease you join the next two stitches together.
A decrease may also be written as 'DC2tog', Double Crochet two together.

This is a Treble Increase. I have placed two stitches in the same stitch loop.

 To make a Treble Decrease;
Make the first part of the next two Treble stitches;

Yarn over and pull through all the loops on the hook, completing the stitches.

An Invisble Decrease is useful especially in Amigurumi where you are trying to create a even fabric. I find it useful as it reduces the bulky lump which is normally left by a Double crochet decrease.

Place your hook through the Front Loop only of the next two stitches.

Yarn over and draw through the first two loops only.

Yarn over and draw through remaining two loops.

Here's what the stitch looks like in the middle of a row.