Expect to make many random choices of squares to sink ships, there aren’t many reliable strategies to use:

Quadrant and Edges Opening Salvo: You’re obviously clueless where to look on your first move. I sometimes plant a salvo in the middle of each quadrant, then I’ll survey the edges and corners. Beware of repeating this opening strategy with repeat opponents as it’s easily defeated if anticipated.

Perpendicular Channels: once you’ve laid down a few misses, look for perpendicular channels the length of your enemy’s undetected target ship(s) and without any misses or previously located ships; then try to hit the intersecting square. This strategy works best for finding longer ships but isn’t helpful for finding the smallest ship (the sub). Any ship could escape detection so don’t ignore single or parallel channels the length of the remaining undetected ship(s).

There are a few approaches to use when placing your ships;

Random: ships are placed randomly, without regard to separation between ships and shore. Randomly placed ships can be difficult to detect where there isn’t a regular pattern for your opponent to reveal.

Pattern: the ships are placed in some regular (not random) pattern. They may be placed symmetrically, in parallel, or perpendicular to each other making a logical pattern - this suggests the pattern could easily be revealed and prosecuted by an opponent to your disadvantage.

Edges: place the ships such that their ends are on, or along, the edge(s) of the grid. The converse would be to avoid the edges altogether, or to place your ships one square away from the edge, but parallel to it. This approach may include either avoiding the corners, or placing ships in the corner. Using the edges, and especially the corners, could lead to easy detection once the edge placements are revealed.

Spaced: arrange ships such that none are touching, or none are within two squares of each other. This placement might help avoid some hits from opponents searching for the direction to follow after an initial hit.

Grouped: this is the converse strategy to the spacing strategy, meaning that at least some ships are placed adjacent (and touching) other ships. This anticipates that once a ship is sunk, the adjacent squares tend to be avoided. Once the initial hit on a ship is made, a player will then search the other adjacent squares looking to sink the revealed ship. If you placed ships adjacent, the opponent may inadvertently hit your adjacent ship. Regardless, this approach is used because the squares adjacent to a sunken ship are often ignored and passed-over. The frequent placement of ships next to each other (adjacent) shows the popularity of this approach for placing ships.