Start with a healthy plant.
The first stage of a plant’s life is about getting bigger and establishing a foundation to make flowers on. Any issues with pests, the environment or plant nutrition that develop early in the growth stage should be identified and corrected prior to flowering.
During the vigorous growth of preadolescence, plants can recover more easily from damage. A sickly plant tends to lack the ability to flower prolifically. In gardens where flowering is artificially initiated, delaying flowering until plants are healthy can increase the number of blooms.
Make sure plants get enough light.
Many plants will grow foliage in lower light conditions than they will flower well in. Although increasing light has diminishing returns after a certain point, a properly lit plant will flower better than an under-lit one will.
Maintain optimal growroom temperatures.
For indoor gardens, make sure the temperatures don’t get too high or too low for the crop being grown, as either scenario can stall plant growth and reduce flower size. A sharp spike in temperature can cause some fruit-bearing plants to drop their flowers, hindering the harvest.
Nitrogen is a necessary ingredient, but while insufficient quantities will hinder flowering, some plants, such as peppers, will grow lots of foliage but few flowers if too much nitrogen is present. Phosphorus is important to flower development, but too much can induce stress even in flowering plants. Consult the needs of the specific plant to determine appropriate nutrient levels.
There are also additive products like bloom boosters and PK boosters available that can have an effect on flowering, both bloom-specific and those that can improve overall plant health, improving blooms as an added bonus.
Induce flowering earlier for an earlier finish.
For outdoor growers, if you cover short-day/fall harvest plants with an opaque sheet on a frame for part of the day to extend the dark periods, you can trigger initial flowering earlier than if the plant was left to its own devices.
Using this method, many plants that would otherwise be unsuitable for an area can be grown even with a short summer season. This is especially useful in areas where fall frosts start early, as plants can be given enough time to mature before the frost arrives, with the added benefit of flowering while still receiving the strong summer sunlight.
Prune some of the blooms.
By removing budding sites that will obviously underperform, the resources they would have used can be divided among the remaining flowers, improving them. It is common to remove some of the flowers from the lowest branches to improve air circulation around the base of the central stem and to prevent the smallest flowers from sequestering growth potential.
Plant more plants.
Although it may seem like an obvious solution, it is often overlooked. A second plant producing the same amount of blooms gives the same result as doubling the blooms on a single plant. While this is heavily dependent on the specific resources available to the gardener, it is often the pimpliest method to improve production.