First you will need to have a ribbon to tie into a bow. Start by opening up a blank 12 X 12, 300 ppi page.This will be your working surface. Using the rectangle marquee tool, draw a half inch tall and 12 inch wide square on your paper. Fill the square with the color of your choice. Duplicate this layer and set the styles this way:

First layer:
Pattern Overlay - Blend Mode: Hard Light, Opacity: 100%, Pattern: Coarse Weave, Scale: 19%
Second layer:
Set Fill to 0%
Stroke - Size: 6px, Position: inside, Blend mode: color burn, Opacity: 53%, Fill type: Pattern, Pattern: Gauze, Scale: 325%
Pattern Overlay - Blend Mode: Color Burn, Opacity: 50%, Pattern: Satin, Scale: 1000%

Merge the two layers and you have a basic ribbon. Of course, if you already have a ribbon, use that instead.

Select a four inch portion using the rectangle marquee.Copy and paste that section. Then copy and paste a different portion of the ribbon. Because of the satin pattern overlay, each selection will be different and will make give your bow a little variation like in real life.

Zoom in so you can see what you are doing, Select the layer of one of the ribbon pieces and go to Edit>Transform>Warp. You will see the handles on the ribbon piece. Notice that at each corner of the piece there at squares and there are round balls between these squares.

With your mouse, grab the top square on the right end and drag it to the top square on the left side. Drag the bottom square on the right side to the bottom square on the left side. Don't worry about how goofy it looks. Do NOT apply transformation yet.

See the two balls on the right side of the ribbon piece that are attached to some lines. These are levers and we are going to use them to pull the piece of ribbon into shape. Grab the top right one and pull it to the corresponding ball on the left. Grab the bottom right one and pull it to the corresponding one on the left. We have a piece of ribbon that is folded in half. Do NOT apply transformation yet.

Now, we need to add a little pinch to the left end of the ribbon. Grab the squares on the left side and move them in towards the middle. There will be two on the top and two on the bottom. Do NOT apply transformation yet.

Lets fluff the other end of the ribbon as well. See the balls that are just to the right and outside of the fold? Move these up and down to spread out the bottom layer of ribbon. The balls that are to the far right will adjust the top layer of ribbon. Move these out a little. Then if you want to adjust any more of this piece of ribbon, you can click and drag the lines and the ribbon itself. This is one of the places where you can add personality to a bow. NOW you can apply the transformation!

Do the same thing to the second piece of ribbon you copy and pasted from the long ribbon. so you will have two bow halves. Remember that in real life do you rarely have both halves of a bow looking identical.

Flip one of the bows by going to Edit>Transform>Flip Horizontal. Line the two bows up end to end.

Now for the middle. Go back to the ribbon we made at the beginning and select a one inch piece and copy it into its own layer. Rotate this one inch piece by going to Edit>Transform>Rotate 90 CW Place the rotated piece on top of the bow halves.

Go to Edit>Transform>Warp again and drag the squares and balls in towards the middle to adjust the ribbon piece to look like a knot. Apply transformation. It may take a few tries to get it as the guidelines hide what you are doing.

Duplicate this knot and place the duplicate layer underneath the first knot. Rotate the duplicate knot a little and then adjust its size and shape to make it look like a layer of the knot. I have changed the color of the bottom knot layer so you can see it better here. It is just a small piece showing from under, but it will make the bow more realistic. You can make variations on this knot yourself. I found it helps to tie a bow and look at it real carefully to see if I can imitate it.

To finish our bow, we need some ties. Use your rectangle selection tool to copy and paste two four inch pieces of ribbon. Again, make each one from a different part of the ribbon.

Rotate the ties around to where you feel they look the best. They will look a little too straight and formal but we will fix that.

Use your eraser tool to erase the parts of the ties that are sticking about the top of the bow and use the polygonal lasso tool to select and delete portions of the bottoms of the ties to make diagonal cuts.

Zoom out so you can see the whole tie. Go to Edit>Transform>Warp and adjust the shape of the tie - pinch the top in and fluff the rest of it. It just takes a little warp here to make the bow look like a flowing piece of ribbon.

Now, some would say the bow is completed. But, lets do just a little more. At this point I group the layers together and duplicate the layer. Then working on the duplicate, use your Burn and Dodge tools to create folds and highlights around the bow. The knot needs some creases, the ends of the folded bow need a little highlight, and the ties could use a little work as well. Since this is a duplicate, you can always start over if you need to. But, this dodge and burn will give your bow that extra feeling of depth. Set the exposure to less than 25% to do this and soften your brushes to 0% hardness.