How to prepare the soil ?

[Annies]

I have planted few of the vegetables & fruit plants like mulberry and guava. All the plants grow well and flower but as soon as the flowers are ready they drop. This is happening to all my plants. Could you please suggest what I might be doing wrong ? And how to prepare the soil ?

[ZandraJoi]

From what I've learned if a plant flowers but doesn't produce fruit it's from lack of pollination. I've seen that happen at some friends home where they sprayed for mosquitoes. The pesticide kills the unwanted bugs but also doesn't differentiate between the good, beneficial ones. So they had no bees. No bees means no pollination.
What kind of insects do you have that are pollinators? Do you see them coming around?