It is also good to have a copy of the layer, in case things get messed up too much.
On Layer Modes And Transparancies…
In the layers palette, there will be a box on the top left side that reads ’normal’ by default.
Clicking on the right side of the box will bring up the modes menu.
As you can see..there are over 20 settings..lots of variation
An entire tutorial can be written on this one menu, so I will not go into great detail.
However…I will state that layer modes are one of Photoshop’s most powerful weapons.
What they do, is affect how layers reflect against each other…
It is much easier to demonstrate than explain.
The first time I stumbled upon this technique, it blew my mind..I will never be the same again. 
To demonstrate…
2. Duplicate cloud1 layer..call it cloud2.
3. Click on the word ’normal’ in the layers palette..it will highlight in blue.
tap on the ’down’ arrow on the keyboard..it will scroll through the modes.
Notice how different the pic looks in each mode…some of it
will look good…some really bad…some of them will make no difference
Thing is though…some of the ugly looking modes can be made to look great.
If you look on the top right of the palette menu it will have a box that reads ’opacity.
This affects how solid or transparent the layer will be.
Some modes that are horrible at 100% can be really effective at 5%
Multiple layers can be stacked endlessly on top of each other..each set to a different mode and opacity..
The results can be stunning.
