1. Where to put your ships
Some people place all of their ships together. This way if someone sinks one of the ships in that group they will move on to another part of the board. I personally don’t like this theory. I believe it is better to place your ships far away.
While it may throw off your opponent at the start that your ships are all together once they figure it out it is all over. They know exactly what area to shoot at in order to hit you. If on the other hand you put all your ships in different areas it is much harder. It is easy to find ships that are next to each other harder to find a ship that is in the middle of nowhere.
2. Know about your opponents.
Every opponent you have will probably think just a little different. They might tend to put their ships on the sides or they might start shooting for your boats in the middle of the board. Knowing what to expect is a good way to win the game.
3. Keep Record of everything
This goes without saying. You should keep record of all the spots you missed and all of the spots that where a direct hit. If you do you will not shoot at the same spot twice and that can really help you.