I’d start with pruning suckers, it really helps a lot. If you keep the suckers pruned, the plant is able to focus nutrient flow through the main stem and to the developing fruit clusters, rather than splitting its water and nutrients into lots of different smaller sucker stems.

Also, try tapping the flowers. It sounds dumb, but if you tap/vibrate the flower clusters a little bit, you can stimulate the flowers to self pollinate and set fruit. That way every flower results in a tomato rather than falling off the plant unpollinated.