The best pest spray is no pest spray.

Do the trees usually bear well? What sort of pests did you have? Are you sure that it was pests that caused the poor set? I certainly wouldn't blanket spray just in case - one of the advantages of home grown fruit is no pesticide residues after all. You could try the old fashioned tar oil winter wash and grease banding and ask again when you know what pest you are worried about.

A good mulch of something organic might help but a poor crop might just have been due to poor weather at setting time or even lack of pollinating insects.. Some trees only seem to bear well every other year anyway.

Well there isn't one, any more than there is a 'catch all' treatment for sick human beings. You need to establish exactly what the problem was for each individual fruiting tree, then take the appropriate action to treat for the problem. Problems can vary on different types of fruiting tree, and range from fungal infections (rust on pears, for example) through to infestations (Plum moth, for instance).

I use a `winter wash` on fruit trees, you can buy it at garden centres and it will kill off overwintering bugs. Can apply again in spring.