The Loop Join for Granny Stitch
The type of joining is great because you are linking your squares (or other shape) as you crochet them. It cuts out an entire step of sewing them all together. The downside is that you won't have a border between each square so make sure to look at your pattern and decide whether it needs a defining border.
[One warning I will give you - make sure to use the same weight and size of yarn and hook for each square. I purposely made the red square a bit larger by adding additional chain 1 spaces in between each 3 double crochet section. When one piece is larger than the other it really really shows and will make your end piece pucker.]
Ok, first crochet a square (check my previous post on how to crochet a square). Now crochet a second square, but don't finish it. Stop at the last side, adding 3 double crochet stitches in the corner.
Chain 1. Now line up your previous square and your new square (make sure the same side is up for both.)
Insert your hook in the corner space of your other square and pull up a loop - pull the loop through the loop on your hook to complete a slip stitch.
Chain 1 and add 3 more double crochet (DC) stitches to your red corner.
Chain 1, Slip stitch in next space of your blue square, Chain 1.
Continue working the pattern on the red square - with 3 double crochet (dc) stitches per space.
And a chain 1, slip stitch, chain 1 to each space of the blue square.
You now have a piece consisting of 2 granny squares. Keep crocheting squares and linking them like the above example until you reach the desired size.
When using this technique you might consider how you will crochet and link your squares. It will be apparent to a view of your finished work, which squares were slip stitched to others so you might consider a stratagy so that it all looks planned. I typically will crochet my blankets in strips -length of widthwise - so that an entire strip with show the slip stitches all going in the same direction.
When you start your next row you will then need to connect two sides of each square to the adjacent two squares. To do this you would use the same technique as above, except you slip stitch in each of the corner spaces of the two adjacent squares before completing the second part of your corner (3dc - slip stitch to 2 corners - 3 dc).
If the above is confusing at all or if you have questions, post to the CrochetByKarin Facebook site and I'll jump in the help you. http://www.facebook.com/pages/CrochetByKarin/134647016599101