Diagonal Granny Stripe Afghan Tutorial

Here are a couple of other samples I made:
I used Simply Soft Worsted weight yarn and an I hook.  Since this yarn has no dye lot, I start with one skein of each color and if needed I may buy a second skein.  Chain 4 and join into a loop.Chain 4 and turn.
Do three double crochets (double crochet cluster) in the loop.Chain 1.  Double crochet into loop.   One diagonal row completed. I know it's a little hard to see it now, but stay with me.
Chain 4 and turn.Do 3 double crochets in the same space. 
Chain 1.  Do 3 double crochets in space. Chain 1.  Double crochet in same space.  Row 2 completed.
Chain 4 and turn.  Continue making sure to put your double crochet cluster in the same space at the beginning and end of each row until we start to decrease.
NOTE:  This afghan will form a square, so when the length of one side measures what you want then begin to decrease. I've done 10 rows increasing just for this tutorial.  Your afghan will be much larger. Decrease:  Chain 4 and turn. 
DO NOT put a cluster in that first space.  Put the double crochet cluster in the next space and continue across the row. End the row by doing chain 1, double crochet in the last space.Chain 4 and turn.  Again DO NOT put the double crochet in that first space.  Double crochet in the next space and continue across the row. 
End the row with chain 1, double crochet in the last space.  Chain 4 and turn. Keep going until you are back to the corner of the afghan.  You end by doing chain 4, double crochet in the middle space.  Chain 1, double crochet.  (I didn't get a photo of the last chain 1 DC, but you can see it in the next photo.)  Tie the yarn off. Here is my sample square.  I think the afghan will need some kind of a border around the edge.  I haven't finished my afghan yet so I'm not sure what I'll use. source