In Australia we are more fortunate than seaside gardeners elsewhere as we are blessed with lots of salt-tolerant natives. Even so it can be a constant battle against the elements to create and maintain a healthy garden. That is unless you follow a few basic tips....
Excess salt is toxic, and when it accumulates on the plant it retards it's growth. This can be counteracted by regularly spraying the plants with fresh water. Then there's constant blasting by sand which has an an abrasive effect on trunks, stems and new leaves, especially on young plants. Protection must be provided for young plants because it may only take a few hours of salt-laden, gale-force winds to badly damage a young garden or slow the growth of semi-mature plants. Strong uninterrupted coastal winds usually means that coastal plants end up stunted and often leaning to leeward. Screens or windbreaks help but don't change the fact that a lot of salt gets onto and into the soil and plants.
The most important thing is that you don't fight the environment but find plants that can tolerate the conditions to protect the more delicate plants behind them. One way of finding out which plants are best suited to various zones is to check out the local flora which is already adapted to the conditions and then pick out your favourites. Native flora are not only able to withstand the conditions but also preserve the local character of the area and because they've evolved with the local birds and insects there's a better ecological balance and so they are less prone to pests and diseases.
A lot of exotics don't like salty, windy coastal conditions but if you want extra colour choose ones that are proven to thrive in these conditions such as hibiscus, snow in summer and lavender. But beware a lot of exotics can 'escape' from our gardens and run rampant through the bush often out competing local vegetation. You must be ever vigilant.
Coastal areas are also extremely fragile. The King Tides and onshore winds can quickly erode beach fronts. Grasses and other tufted plants are extremely important in stabilising shifting sands. Most of Australia's coast is made up of sandy soil so it is very free draining and often low in nutrients. It requires regular applications of compost to keep them nutritious and the garden blooming. On the coast it is not ideal to use large amounts of fertilisers as they may end up creating problems in the ocean. Insects, pests and weeds don't much like the salt air, so if you choose the right coastal plants, mulching to retain moisture, all that's left to do is regular watering.