Tips on Layers:

To collapse or merge layers - You may find that at times you will need to merge two or more layers. To do this go to the layers palette, and click on the arrow on the top right corner, then select from three options: "Merge Down," "Merge Visible," or "Flatten Image."

Merge Down means that the layer you've selected will merge with the layer below. Merge Visible will merge all layers that are viewable (have the eye icon turn on). Flatten Image will merge all layers, regardless of visibility.

Layer Opacity - can be adjusted at the top of the layers window. Experiment with this feature according to your ideas.

Adjustment Layers - were previously introduced. Make sure to familiarize yourself with this palette found at the bottom of the layer window. As you may remember, this features allows you to adjust color, contrast, as well as threshold without committing your image to the effect.

More Brushes:

History Brush - restores pixels to a previous state. You can select this state from your history palette by click on the corresponding square on the left handside for each action.To use this tool, select the history brush from the tool palette menu, then select a state from your history, and apply to the area of your image as you desire. Please note that this is specific to the history of each layer. You cannot apply the effect of one layer to another layer, because each layer has a specific history.

Art History Brush - Useful to create an effect based on effects you've applied previously. It's done with stylized brushes. This tool works on all layers. Once you select the tool from the Tool palette, click on the desired state, then select brushes and adjust the brushes options at the top menu.

Making a workpath from Selections made with various selection tools - as you've learned, you can create a selection with your lasso tools. If you are working on a selection that needs to be very detailed, then you may want to begin with a lasso selection and once you are satisfied with this one convert it to a path selection for greater control, with no worries for masking. To do this, first select your object or area with any of the lasso tools, then go to the path palette window and at the bottom menu click "Make work path from selection." (It's the circle with extending anchor arms on its sides.)

Gradient Tool - useful to create color change from left to right or in circular form as well as other shapes (you can find these at the top photoshop menu once you've selected the tool). Select the tool from the tool palette, then select your desired colors from the color menu at the bottom of the tool palette or make the menu visible by selecting at the top of your computer screen: Window :> Color. Apply gradient to a mask or a selected area of your choice.

Styles - preset effects that can be applied to an area or layer that you select. To access Styles, go to the top of you computer screen and from the menu select Window > Styles, then choose the style of your choice. To create your own style, create a layer effect by selecting one from the bottom layer menu (the button contains an "f"), then when you're satisfied, on the layer effect window, click the button "save as new style"