Here's something expected from you to outcome from this tutorial.
1- When you have your desired design done one Photoshop, go to the Tools bar and click on Edit in ImageReady (or click Shift+Ctrl+M)
2-Now you have a similar interface as the one for Photoshop. The Animation bar should appear by default, if not press F11 or simply go to Windows and tick on Animation.
3- Select your desired layer(s). For the sake of this tutorial, I chose the Text layer.
4-Go to the animation bar and duplicate the current frame. Then, go to the Text layer and change the Opacity to 80%.
5-Keep repeating step 4 but with different descending numbers (by 20% in each layer in this tutorial). Once you reach 20% Opacity, make the next frame's Text layer to be 10% instead of 0%. After that, use ascending numbers and stop at 80%. ( because the Text layer in frame 1 is 100%)
6-Now you're almost done and you can play your Animation.
7-If you're not happy with the animation frame time you can always change each frame's timing by clicking under the frame display layer. In my final image, I made the delay on each frame to 0.1 second.
8-Save your animation by going to File, Save Optimized As ( Shift+Ctrl+Alt+S) and choose your destination to save. Make sure that the format is of type GIF.
End of the Tutorial.
Please if there is anything that is not clear, then point it out. P.S: show me your work please :D