This tutorial was created long time ago too. I will make a better version of this if I have the time. Quite busy with current activity and tests. So enjoy.
This was created using Adobe Photoshop 7.
1) First we create a new file. For this i use 500X 500 px.
2) Create a new layer (we will name this layer star layer), fill it with black and use noise filter Filter>Noise>Add noise.
3) Then we will adjust the brightness and contrast. Image>Adjustment>Brightness and Contrast
4) This is the current effect.
5) Next we will create another layer (we will name this cloud layer) and use Cloud Filter. Filter > Render > Cloud
6) We shall use another filter. Filter > Render > Difference cloud
7) Tap Ctrl + F to repeat difference cloud. We shall see the cloud layer is getting more messy.
8) After that,,, we will use blur. Filter>Blur>Motion blur.
9) To create the wavy effects, we use wave. Filter > Distort> Wave. You could use the value i used,,, click randomize to see different effect. But use only 1 generator, we dont want the cloud to get too messy.
10) Next, set the cloud layer to Screen.
11) Now, we are going to darken the cloud layer. Go to Image > Adjustment> Levels. Drag the middle bar to the right,,, u could judge it yourself.
12) Current effect.
13) Choose this brush and use black colour, push the flow to around 20%.
14) Then colour the cloud layer to get rid of any unwanted clouds, like i did in the picture around the arrow head.
15) We dont want our cloud to look dull, do we? So we go to Image > Adjustment> Hue and Saturation, remember to hit the colorize tick.
16) Now we have a colourful cloud,,, next, using the same black brush, colour on the star layer to get rid of unwanted stars,,,
17) Then, pick a size 5 brush, set the size jitter to 100%, remember to change the flow to 100%,,, dot a few stars on the star layer to add stars,,,,
18) Final effect.
19) Add another cloud layer to a colourful nebula clouds.