The Fish Base is a common starting point for many easy origami projects, including the Lucky Frog origami.
Easy Origami: Fish Base
Start with the Kite Base. Unfold.
Fold both sides to the center, forming a point at the top. Unfold.
Fold in half, bottom to top. Unfold.
Pinch the left and right sides and collapse to the center along the diagonal fold lines. Fold the flaps up.
Here is another view of step 4.
This is the finished fish base.
This origami fish base how-to is excerpted with permission from "Crease and Fold: Innovative Origami Projects Anyone Can Make" by Suk Song, published by Potter Craft.