Tides

The moons gravitational force produces a 'bulge' in the sea exactly in the line with the moon itself, which is why oceans experience. What is not so well know is that's there's an equal bulge on the opposite of the earth. The two bulges are the low water.

The earth spins around on its own axis underneath these two bulge's and every point on the ocean's surface will experience at least one of these bulges every day.
Throughout the time it takes for the earth and moon to go round each other (a lunar month), the moon has four phases: opposition, quadrature, conjunction and quadrature (again).

The sun has a smaller influence on the tides, but it does produce bulges in the ocean just as the moon does. So when the sun and the moon are lined up (in opposition or conjunction), their tidal effects are added together, which makes for some big bulges in the same place, the cause of spring tides. When the sun is at an angle of 90 degrees to the moon (i.e.: in quadrature), they create bulges at right angles. The water is evened out all over the earth's oceans, producing neap tides.

Instead of just going in and out, tides tend to swirl around imaginary points called amphidromes. This is due to the rotation of the earth, and the Coriolis factor. The greater the distance from the nearest amphidrome, the greater the tidal range.

There are no rules, although most areas have a normal, semi-diurnal (two tides a day) regime and the surf is always affected by them. Europe experiences many tidal extremes particularly around the UK and in the North Sea. Shallow, narrow straits of water can greatly increase tidal ranges. The 12.6m (38ft) tidal range at the top of the Bristol Channel is the third largest in the world.

Most surf spots only work on certain heights of tide: too low and the wave may close out, too high and it barely breaks. Some breaks may be twice the size at high tide, while the adjacent beach break are more powerful at low tide. A lot of spots get bigger on the push of the tide possibly due to the incoming tide superimposing its motion on the sells, making them move faster, many rivermouth waves can be impossible to surf on the outgoing tide, which will drag you past the take-off zone.