Some types of tomatoes can be pollinated well by wind or shaking, but others do not. They release pollens in responding to viberations at a certain frequency only, which is usually the frequency of the bee's buzzing (bumble bees are the best pollinators to tomatos).
When you see this problem, use an electric toothbrush ( use a type of Sonic Oral-B with three viberation modes and the middle mode is close to the frequency of bee's buzzing) to gently touch the flowser stems. During the viberation, you can even see pollens bursting out from the small hole of the flowers. Since then, no flowers fall, and magically, each turns into a fruit.
To encourage blossom, you need to feed them with fertilzers in high potassium and phosphorous. If you are looking for fertilzers specially made for tomatoes, you'll notice that they conatin high ratio of potassium and phosphorous. Also, you'll need to pinch off suckers at bottom and sides to force the plant to provide more fruit on main branches. They will put less energy into growing vines and more into producing flowers and fruits.
When you water your plants, run the hose at the base of the plants. Do not water tomatoes overhead. Do not allow water to splash from the soil to leaves. Overhead watering or splashing can creat blight (fungus) on your plants. Water thoroughly and then hold off for several days before rewatering. Lacking for water may stunt the plants and discourage blossom and fruit forming.
However, too much water and too much nitrigon will result a lush foliage growth with less blossom and fruits, and produce less tasteful fruits and cause slow ripening. This is the typical mistake that many home gardners make.