Standing double crochet stitch gives a very neat way to join on a new yarn to a round or row where you need to use double crochet - also referred to as DC in crocheting terminology. It means that you do not have to join on with the very clumsy looking slip stitch followed by 2 or 3 chain stitches. The chains are there to take you up to the height of a normal double crochet stitch but no matter how neatly you work these chain stitches, they never look quite right on the crocheted piece. In fact, it always tends to look like you have a gap or hole in your project.
This special form of the double crochet stitch provides a really easy and neat way to start a new row or round and this tutorial shows you how to add it on and join it to a project with a new color of yarn. Once you get into the hang of using this particular technique, you won’t want to go back to using the standard chain stitches for this method again. There are lots of photos to follow along with the following written tutorial.
Please note that this tutorial refers to the US version of the DC (double crochet) stitch which is the same as the TR (treble crochet) in UK crocheting terminology. 
1: Make the Initial Slip Knot
I recommend that you test this technique out on an existing project where you can easily add a new round to practice. Something like a granny square would be ideal. I tested mine with a sunburst granny square pattern where the colors get changed in every new round.
Another tip is to use a slightly larger crochet hook than normal so that you can easily see the all the individual loops and sections of yarn as you are working. You can always pull out this practice section afterwards so as not to spoil your project.
With a new color of yarn, make a slip knot to start as you normally would and push it on your hook.
Pull the end of the yarn over to the right hand side. Now loop the working piece of yarn on the left over the top of the hook from the back to the front, exactly as shown in the photo.
2: Join the New Yarn to the Project
Now you have the yarn in the right place, insert your hook at the point of your project where you want to make the standing double crochet stitch.
With the hook inserted, take hold of the working piece of yarn from the back of the hook. Pull it over the top of your project and across to the front of your hook on the other side.
3: Catch the Working Yarn and Pull Through
Pull the hook gently through the project, making sure to catch the working yarn as you pull it through. The hook will pull the strand of yarn through from the back of the project to the front where it will create a third loop.
4: Check the Number of Loops
You now should have a total of 3 loops on the main shaft of your crochet hook as shown in the photo above.
5: Make a Loop Around the Hook
Take hold of your working yarn again and wrap it over the hook from the back over to the front as demonstrated in the photo.
While you do this, it helps to keep hold of the end of the yarn as shown over on the right at this point. I have it secured with my thumb in the photo.
6: Pull the Loop Through
Pull the loop that you just made through the next two loops that are already on your hook.
7: Make Another Loop
Wrap the working yarn around the hook from the back to the front of the hook again to make another loop. Secure the tail or yarn end with your thumb as this helps to keep the stitch neat and tidy as you are making it.
8: Pull Yarn Through the Remaining Loops on the Hook
Pull the loop that you just made through the last two loops on the shaft of your hook. This has now made standing double crochet stitch as shown in the photo. It looks thicker and neater than using the alternative method of chain stitches worked upwards and it will match up in height with the rest of the stitches.
Continue Working the Rest of Your Stitches as Normal
From this point, you can carry on making double crochet stitches and other stitches required for your pattern as per normal. This method blends in better with the overall project because it is the same size and shape as a normal double crochet.
In the case of a motif such as a circle or a square where you need to join a round back to that initial stitch, you just work a slip stitch into the top of the standing double crochet that you created. It is very easy and neat to finish off that way. I like to use my Chibi darning needles to sew in all the untidy yarn strands at the back of my work.
The circular motif shown here is from my Sunburst Granny Square pattern. 
Video Demonstration of this Technique
In this excellent video demonstration, the presenter first shows the traditional joining method which uses 3 chains to get up to the height of a normal double crochet stitch. You can see in the video why that older method doesn't look good. It essentially creates the look of a hole in your project.
She then carries on to slowly show her technique twice in the video. It varies only a little from mine in that she doesn't make a slip knot right at the start with her yarn. So you can choose the variation that you like the look of more when you need to use this to start a new round or row.
Use this Method for a More Professional Look
This method certainly makes for better finished projects and gives a much neater and more professional look to your crocheted item. You can now apply this method to many crochet stitch patterns instead of using chains.
How your finished item looks is especially important when either selling your work or giving it as a special gift. Hopefully this has inspired you to want to go and try this brilliant technique for yourself.
Image Credit: all images on this page belong to the author of this article, Marie Williams Johnstone