Avoid sending ships unless you will get a lot of points, or you can prevent your opponent from getting a lot of points.

If all the ships are full, prefer picking up new stones over sending ships. Except if you have stones and your opponents have none.

Early in a two player game consider sending a ship to the obelisk if you have no stones on it, but your opponent has two. Then every time they have two, and you have none, send their ship to the obelisk. Meanwhile make your points from other destinations.

The blue Market card Level is often a low priority card because of the above advice to avoid sending ships.