Smoke Tutorial for those who are using SAI, or Photoshop! This should work generally the same for either program, but if you have any questions, just let me know~
1) Draw some blobs using the pen/brush tool at low density/opacity.
2) Make a new layer above that and draw some darker colored blobs at the same density/opacity.
3) Take the blur tool at medium density/opacity and low pressure/persistance and lightly go over both layers to blend them together. You can do a lot, since the blur won't be so strong, and get a result that you like. Also, change the master opacity of the layers to make them more see-through.
4) For SAI users, you can take the Oil Water brush and set it to very low density and brush over each layer. For PS users, there should be a brush preset that is oil water, or something close to it. Just look at the names for them to find it.
5) Make another layer and use some darker colors than before with the same brush/pen settings. Place this layer below the first one.
5.5) I didn't show this step, but I also used the Water brush on very low density and went over each layer.
6) Now, take the eraser and set it on a medium size with low density/opacity, and stroke over some parts of each layer to give it that...smokey feel. xD; I don't really know how to explain this other than trying to make it look like the picture. D;
6 optional) You can also blur the three layers to make it more blended if the smoke has been in the air longer, or if it's just coming out of the pipe/cigarette/etc.
Aaaaaand, that's how you do it! If this was helpful, let me know! And if you make something using this tutorial, show it to me! <3 I'd love to receive feedback, also, if there's anything that doesn't look/sound right. :3 Thanks!