Shake it so the pollen gets shared with all the other flowers.
You can use something called Blossom Set to get more fruit.
Add some Epsom Salts.
Prune off a quarter or so of all the leaves after it's set the tomatoes.
Cut off long vines that don't have tomatoes set on them and stick them in water or soil, they root nicely for me. This works if you find one in the bunch that looks different, or you want one a friend has, etc. Should you have a green house you can grow them all year round since they are perennials. They are usually grown as annuals since they are tender and freeze out easily, but in the tropics they can grow all year round.