Smoke

Ok, i wrote this particle effect code and it's basicaly meant to look like smoke. It just ends up looking like a lot of grey blobs that don't look anything like smoke...
I'm using a grey blurry sprite as the main_particle. Does anyone have any ideas anout how I could make this a bit more realistic.

Here's the code:

Function createparticle(player)

	p.particle=New particle
	p\entity=CopyEntity(main_particle)
	p\x=EntityX(player)
	p\y=EntityY(player)-1
	p\z=EntityZ(player)-1
	p\time=Rand(1400,2200)
	p\timer=MilliSecs()
	PositionEntity p\entity,p\x,p\y,p\z
	p\speed=-3
	p\alpha=1
	
End Function 

Function updateparticles()
         
        Local random=Rnd(-0.5,0.5)
	For p.particle= Each particle
	p\alpha=p\alpha-0.1
	EntityAlpha p\entity,p\alpha
        MoveEntity p\ent,random,random,random
	If MilliSecs()>p\time+p\timer Then
	FreeEntity p\entity
	Delete p.particle
	EndIf
    Next

End Function