Create a new document that is the size of your desktop screen. Mine is 1280x800. Select the blend tool and give the background a brown (#d7aa82) to black radial gradient. Use these settings:
Apply the gradient from the center of your document to close to the outside, holding down Ctrl/CMD as you do so.
Now we need an image of a pumpkin. I am going to use this one, but you can use whatever you like. File > Open as Layers. Select your pumpkin. It will open on a new layer in your document.
Render your pumpkin. You can do this using a variety of methods, so do it however you like. I am going to render mine using the path tool. In my image, the pumpkin is a bit flat. I am going to use the scale tool to make it a bit taller.
Now we will recolor our pumpkin so it's the color of traditional carved pumpkins. Select the entire pumpkin except for the stem. The easiest way to do this is to use either the lasso tool or the paths tool and select the stem, then invert the selection. Go to Select > Feather. Feather it by one. After you have done that, go to Colors > Colorize. Apply these settings to get an orange hue, or you can play around with the sliders until you get something you like.
With your selection still active, invert it by going to Select >Invert, or Ctrl/CMD-I. Now you should have only the stem selected. Go to Colors > Colorize.
Let's increase the darkness in the pumpkin by going to Colors > Levels. Adjust mainly the middle and right sliders to darken the pumpkin, but don't darken it too much.
Create a new layer above the pumpkin and name it "sketch." Using the brush tool, draw a quick, rough sketch of your jack-o-lantern's face. You can even use the pen tool and then stroke the path you created.
Create a new layer above the sketch layer and name it "fill." Now using the Magic Wand Tool, select inside the sketch. Hold down the shift key as you select so you can select more than one area at a time, eg. the eyes, nose, and mouth. Now grab the Bucket Fill Tool and and fill the selection with black on the "Fill" layer we created earlier. Deselect and hide the "sketch" layer.
Now we'll create an inner lighting effect. Create a new layer and name it "radial gradient overlay." Apply a radial gradient to it that goes from an orange (#ff5a00) to a dark brown (#572b04) with the selection of your fill. (If your fill isn't selected, right click it's layer, and click Alpha to Selection.) Set the layer mode to Multiply. Create another new layer and name it "pattern overlay." Download this pattern and place it inside your fill's selection. Set the layer mode to Multiply.
Bring the pumpkin layer above all of the layers. Alpha to Selection on the Gradient Overlay layer. Go back to the pumpkin layer and press delete. Everything should be deleted where the eyes, mouth, and nose are, letting the textures show through.
Now we'll add in some light sources. Download this photo of a candle and open it as a new layer named "candle." Make a quick selection around it with the Lasso Tool and go to Select > Feather. Feather it by about 30 pixels. Copy/paste onto a new layer. Delete the previous candle layer.
Now we will add the candle by changing the layer mode to Screen. Put the candle layer below the pumpkin layer, but above everything else. Your candle should be inside the pumpkin. Duplicate the candle a few times if you want to.
Bring back the "sketch" layer and drag it above the rest of the layers. Unhide it. Draw some more lines on it to give it depth.
Select the new areas with the Magic Wand Tool and create a new layer below the pumpkin layer called "depth." Fill the selection with black. Hide the sketch again. I actually had to do some fixing with the eraser and brush tools to get it to come out exactly like it did, and you may need to do the same as well.
Now we will add a pattern and gradient overlay like before. This will give it more depth and texture. Again, right click, alpha to selection on the depth layer. Create a new layer named "gradient overlay depth." Click the gradient tool and apply a gradient like before. Lower the opacity just a bit.
Create another new layer named pattern overlay depth. Open up that texture we downloaded earlier and place it in the selection. Set the layer mode to Multiply.
Now we'll add some light details around our pumpkin. Create a new layer and name it "light details." Get a small, soft brush and paint a few lines close to the carving borders and then use the smudge tool to make the lines softer.
Create another new layer and name it "depth adjust." Using a soft, dark brush, paint over some of the depth areas in the carvings so you have inner shadows for each hole. I also went in and added another candle inside the pumpkin.
Now we'll add a nice background. Create a new layer and place it underneath all of the other layers except the background layer. Name it "clouds." Go to Filters > Render > Clouds > Solid Noise. Raise the detail to about 10 and click ok. Set the blending mode to Dodge. Create a new layer above it and name it "fractal." Go to Filters > Render > Nature > Flame. Get something about like I have below. Duplicate it, rotate it, and place it in a few different spots on the canvas. Merge all of the fractal layers down to one layer, and be sure the layer mode is set to Dodge.
Afterward, select your pumpkin layer and go to Filters > Light and Shadow > Drop Shadow. Set both offsets to zero, the blur radius to 8, and don't allow resizing.
Select the fractal layer and go to Filters > Blur > Gaussian Blur. Leave the values at 5 and press ok. Merge the fractals with the cloud layer and set the layer mode to Dodge. Rename the layer as "Bg1."
Get out the Lasso Tool and and select a good size area in the Bg1 layer. Go to Select > Feather. Feather by 20. Copy and paste it just above the first background layer. Name this new layer "Bg2." Go to Colors > Colorize and give it a red hue. Change Bg2's blending mode to Overlay. Place it like mine below.
Do this again, but instead using a green hue.
Notice that our pumpkin has a dark shadow on the left side. We are gonna try and keep that same lighting effect in our final outcome. Create a new layer above all of our background layers. Make an elliptical selection like mine below:
Go to Select > Feather. Feather by about 150. Fill the selection with black. Get out the scale tool and flatten the black area a bit. Lower the opacity to about 70%. Place the black area under the pumpkin, but to the left a bit.
Now we will add a surface for the pumpkin to sit on. Create a new layer named "floor" just above the background layers. Fill it with black. Right click the layer and select "Add Layer Mask." Select the first option and click ok. Get out the rectangular selection tool and select an area on the bottom that will serve as the floor. Ctrl-I to invert it. Fill it with black. Your pumpkin should now be on a black floor.
Create a new layer called "ground shadow" and place it above all of the other layers. Get out the elliptical selection tool and make a selection underneath the pumpkin. Feather it by 100 pixels and fill it with black.
Now on the same layer, get out the Lasso Tool and draw an irregular shape following the pumpkin's shape. Feather it by 20 pixels, then press delete.
We're almost done. Let's add some more details, shall we? Duplicate one of the candles and name it "front candle." Bring it to the top of all the layers in the layers palette. Place it like I have in front of the pumpkin. Go ahead and duplicate it, while making it smaller to add another candle.
Get out the Burn Tool and the Blur Tool. Use them on the candles to improve them.
I also decided to add another candle on the other side of the pumpkin.
Now we'll add a reflection to the entire thing. First, select the three candles in the front. Duplicate all three layers and merge the duplicates together. Set the layer mode to Screen. Go to Layer > Transform > Flip vertical. Move the layer underneath the original three candles as if it is a reflection. Right click the layer and select "Add Layer Mask." Use a white and black gradient to make it fade out.
Do the same reflection technique for the pumpkin and the other candles.
Save it and you're done!