If you like to depend totally on biological control against pests then you need to get some tools such as solar panels and light emitting diodes (LEDs). Also if you like to use on grid system then you can use LEDs and connect them directly. So they will play an important role to attract predators and parasitoids to the harmful insects and mites exposed to different colors of LEDs.It is all about allelochemicals system.LEDs created a new system depends on direct calls from preys to their predators to come and eat them.Besides,LEDs have good effect even on exposed plants.You can know more through my published papers at my page here on Researchgate. If any outbreak happen then you can even connect or separately spray any natural product or microbial compound against insects and back to LEDs.With that full system you can just depend on biological control  without any need to chemical pesticides.

There are many safe chemicals (green label). Exclusion and prophylactic means are better than meddling with curative measures. Everything depends on target pests.

Basically, the field performance of Biological control has often been unpredictable and too variable for large-scale use. Biological control based on integrated pest management can be predictable and pre-competition with chemical pesticides.

No single system is the answer for managimg any pests for that matter. Best and sustainable solution will be Integrated  Pest Management (IIPM), which vary as per the crop, and location for different pests.

Develop a sound IPM system.

You need to have a good understanding of the population dynamics of your pest and the available natural enemies first. Also make sure that you have the whole community participating in your programme.

The answer to your question is both yes and no. I know some growers who are 100% biological and are doing well when others are not. The most important thing to do is research the project fully. Talk with others first and find what they are succeeding or failing at. Once you have all the fact you are comfortable with then start with one pest and start integrating them into your specific crop. You will have failures, I had  failures but that is how we learn what works for us. Starting small and talking with other growers and the companies that supply the biologic agents to you will help in succeeding. Remember that there may be times that chemicals are need, this is not failure. By changing to biological controls you will find that the chemicals work better than before when you do need to use them. 

Even though the question is very broad, as stated in most of the comments above IPM would be the strategy.

To further fine-tune the question, in order to use biological control intensively for already established crop and considering the biology,ecology and damage of the major pests well understood, it should start with a systematic scouting and monitoring to better understand the population dynamics these pest/s. It is also important to know the pesticide spray history as it will determine the establishment of the biological control agents.

If the above basic information is properly established, it is possible to look for potential biological control agents targeting different life stages of the key pest. At this level it is possible to critically look for a way to consider biological products that can possibly have effect on more than one life stage or one pest. This can assist to design a reliable biological control strategy that takes in to account the occurrence of other secondary pests as the intensive use of pesticides will be avoided and/or softer pesticides will be used.

Once the products are know and properly designed it is essential to investigate the temperature and RH to be conducive for the establishment of the bicontrol agents. It is also recommended to apply some cultural practices that can support the biocontrol agents. If the population is completely checked then it is a matter of properly monitoring the population and treat the hot spots accordingly.       

First, reduce/minimize synthetic pesticide use.

Second, increase biodiversity (e.g. various forms of intercropping or strip-cropping)

This is not an easy or short topic to answer.

I would suggest developing a good working relationship wit on of the producers of biological control methods. These companies are a great resource to use.

That being said you need to research the insects you are trying to control. Know their lifecycle, host plant and what natural occurring organisms are available to control them. It will be very important to look at the minor pests also, these tend to become a larger problem once the synthetic pesticides are reduced.

The crop you are treating needs to be detoxified. The synthetic chemicals may not have an effective residual for the pests but still may be an issue for the biologics. The suppliers have side effects manuals on their web sites and as apps that can help you. The use of bio-pesticides, botanical extracts and plant safe oils are usually a safe bet when switching over.

Be persistent and don't get discouraged. There will be times they don't work as intended, especially at the start of a new program. I have seen may people have difficulties at the beginning and almost gave up. Those same people have very successful programs. I hope that helps, feel free to contact me if you wish.