The first trick (learning from my own mistakes) name you layers something that makes sense to you. Don't let them stay "layer one, layer two and layer one copy". You will find that you will have more layers than you originally plan for, and not having relevant names makes it difficult to work with the layers.
Keep in mind what you are trying to do: if you want to move images around on a color background, keep your image that has had the original back ground a separate layer from the background layer.
Keep text a separate layer from your images.
Remember that when you duplicate a layer, you duplicate all of its attributes as well... so if you have an image that you have applied a drop shadow to and you duplicate this layer, the drop shadow will be duplicated with the image layer.
Always save a .psd file (that keeps all of your layers as is) along with your flattened file (jpg, eps etc) there will always be future changes and once you flatten you will not have the ability to easily move items around because it will be one image, as opposed to several separate images.
When you copy and paste - it will automatically create a new layer. When you click and create new text, a new layer is automatically created. However, if you add color, delete or add shape boxes, they will be added to whatever layer you currently have selected.