Because 60% of all emerging infectious diseases are zoonoses and because animal farming is one of the main contributors to antibiotic resistance, one of the most effective ways to prevent pandemics seems to reduce animal farming and hunting.
WHO “warned in its 2007 report that infectious diseases are emerging at a rate that has not been seen before. Since the 1970s, about 40 infectious diseases have been discovered, including SARS, MERS, Ebola, chikungunya, avian flu, swine flu and, most recently, Zika.”  Could the increase in emerging infectious diseases have to do with the increase an intensification in animal farming? The number of farmed animals almost quadrupled in the last 50 years . The main rise was in poultry birds (483%), which were the leading cause of the H5N1 epidemic in 2003 (455 human deaths) and the H7N9 outbreak in 2013 (616 human deaths). Farmed sheep and goat populations swelled by 156%, and cows and buffaloes 147% during that time. Cows were responsible for Variant Creutzfeld-Jacob disease (‘mad cow disease’/BSE) which claimed hundreds of human lives.Correlation is not causation, but as Al-Jazeera showed in March 2020, most epidemics had to do with animals (see graph below). A widely-cited article in Nature notes that 60% of all emerging infectious diseases are zoonoses, i.e. either came from wild or farmed animals, or animals can at least transmit them.
Larger version - Source: 
‘Species distancing’: No farming and hunting of animals
I propose two measures to reduce epidemics: Not farming and not hunting animals. These measures would block the main routes of transmission from animals to humans. According to CDC, these are contact with bodily fluids of animals (most common in farming, hunting and animal product processing), food (think salmonella in eggs, E. coli from contamination with faeces), and bites and waterborne transmission. Only bites and waterborne transmission would not be solved.
Preventing animal husbandry is also necessary to prevent antibiotic resistance. Yes, not only viruses, but also bacteria can cause pandemics. Take meningitis: “In 1996, the largest meningitis epidemic ever recorded, in terms of the numbers of affected people, occurred in West Africa. An estimated 250,000 people contracted meningitis, and 25,000 people died of the infection.”  “Neisseria meningitidis [a bacterium] is the major cause of seasonal meningitis epidemics in the African meningitis belt.” The more animal products humans consume, the more vulnerable they become to antibiotic resistance. In 2017, 26% of all antibiotics were given to livestock in the UK. The percentage in the US is estimated as high as 80% (and in most other countries, antibiotics given to animals are unfortunately not tracked). The “WHO is recommending that farmers and the food industry stop using antibiotics routinely to promote growth and prevent disease in healthy animals.” Might the WHO proposal not be an unnecessary and unrealistic extra step? After all, its implementation would hurt profitability or animal welfare (because farmed animals would fall ill easier unless one gives them more space). Reducing animal farming and transitioning to plant food seems a more painless and safer alternative that also has other benefits for global public health (e.g. cancer from red and processed meat).
The following are questions I was unable to answer with a 1-hr Google search. Please provide comments if you have ideas on who could answer the following questions:
- What diseases were spread by farmed and hunted animals and which are likely in the future?
- What is more effective, reducing contact with wild animals (“banning bush meat”, closing ‘wet markets’ as widely proposed) or reducing farming?
- What share are animal-to-human zoonoses in the 60% zoonosis number?
- What share of human infections with zoonoses occur through bites and waterborne transmission?
- What level of reduction would be how effective? I suspect that contact reduction and pandemic risk reduction are positively correlated. However, what shape could the following curve have?
Larger version - Source: Own imagination. Risk of pandemic of 1 corresponds to the current (2020) risk of a future pandemic. Restriction in contact with animals is from 0 (no restriction) to 1 (no animal farming and hunting).
 Own calculation (see Google sheet) using data from UN FAO 2019. Calculation of the number 2.7%: In 50 years, the number of farmed Poultry Birds, Sheep, Goats, Cattle and Buffaloes grew by a factor of 3.725685523 ≈ (1+0.0266558)^50
 About emerging infectious diseases (EIDs): “EID events are dominated by zoonoses (60.3% of EIDs) “- Jones KE, Patel NG, Levy MA, et al. Global trends in emerging infectious diseases, Nature, 2008, vol. 451 7181(pg. 990-993), online at https://www.nature.com/articles/nature06536
 And vice versa, which may also contribute to human pandemics by leaving human viruses and bacteria to mutate in large biomass stocks, stocks that are much larger than the 7bn humans we have (For wild animal biomass and population estimates see Brian Tomasik’s article)
 UK One Health Report, 2019, p. 11. Calculation: 26%=281.6/(491.0+281.6)*72% (the latter figure being the share of livestock in all animals) WHO: Stop using antibiotics in healthy animals to prevent the spread of antibiotic resistance WHO: Q&A on the carcinogenicity of the consumption of red meat and processed meat; NHS: Red meat and the risk of bowel cancer