There are a lot of algorithms that you can do on a Rubik's cube. These are a few of my favorites.
Superflip (Flip all edges)
(M U')x4 y z' (M U')x4 y z' (M U')x4
For larger cubes start with the outside layers and move in (So for the 7x7 pictured do the M move by moving all 5 internal layers down, then U' on the top layer. Then move in by doing the M move with the inner 3 layers and U' with the top 2 layers.