One of the many fun aspects of rock pooling is meeting other people on the beach who are interested to see what you have found. After showing people the variety of animals we had in our little photographing tank, many of them seem shocked at the wide variety of animals available and often state they haven't found anything but shore crabs and shanny.
While there are many different types of fish and inverts to be found along the coasts it helps if you know where to look and what to expect. Some species are found in a wide range of habitats, such as Shanny's, while others can only be found amongst specific types of substrates or areas, such as Clingfish.
In open rock pools fairly high on the shore line, I've found numerous species of fish which includes Shanny, Painted goby, Rock goby, Two spotted goby, Montague's blenny, Giant goby, Sand goby and common shrimp. All of these species were easy to spot as you walk by rock pools. They tend to dart for cover as soon as they see movement above. Once I've spotted a pool with a fish in it I would crouch down low and wait for a short period of time The fish will come back out into the open where it's fairly easy to catch provided the pool doesn't have any deep crevices for the fish to quickly escape into. Don't make the assumption that anything that darts is a Shanny or common species of fish!
Under larger rocks (around the size of a dinner plate) that are in an area with a small amount of water flowing by has yielded various invertebrates such as shore crabs, squat lobsters, brittle-starfish, starfish, snails, edible crabs and more. I have also found some fish under these rocks such as shanny's, pipefish and clingfish. Remember to return the rocks to their original positions once you are done as these animals depend on the cover they provide for their survival.
I have also found a wide variety of fish in areas where bladderwrack is exposed during low tide. Some of the species I've found by carefully lifting the algae from around the edges of these rock pools include scorpion fish, goldsinny wrasse, corkwing wrasse, rockling, and two spot gobies.
Sandy bottom beaches and rock pools have flatfish/dab (good luck catching these), dragonets, sand gobies, shrimp, crabs, snails, scorpion fish. I've even found a couple scorpion fish by digging under the sand with a net and sifting out the contents. Look for slight depressions or bulges in the sand that look different from surrounding areas.
Basically it's possible to spot an abundance of life in any location if you are patient and able to look carefully.
Another consideration is looking in the rock pools at various times of the year or after major storms. Different species of fish breed closer to the shorelines at various times of the year. I've generally found that the younger wrasse are found hiding under bladderwrack in fall and winter while mullet fry have been found swimming in open pools earlier in the spring and summer. After a large storm I've found sand smelt fry taking shelter in shallow rock pools until the weather calms down again.