While mildew can be controlled with fungicides, The easiest prevention is mildew resistant cultivars. Bugs are a different story. Sanitation helps; Destroy their overwintering sites by turning under all plant debris and planting a cover crop like rye. even so many of them are migratory, in which case, identify the pest and its life cycle and hit with a specific pesticide at its most vulnerable point. Just don't go blasting away with a shotgun when a BB gun at the appropriate time is more effective. Read up on IPM methods.

The best preventative measures for disease, fungal and insect attack are good soil husbandry and selection of appropriate crops/cultivars. That's because plants that are thriving and healthy are more resistant to disease and often less attractive to pests than stressed plants.

Other than that, there's no magic recipe that I know of.

Some people do spray fungicides 'pre-emptively' in their home garden. I guess one of the reasons for this is that many 'milder' fungicides like copper, neem, baking soda, milk struggle to eradicate fungal diseases once they're there.

The reason I don't is a) in my garden things like PM only show up late in the plant's life, so I can keep on top of it with neem/seaweed spray until the end of the season.
b) all pesticides/fungicides have the issue of resistance lurking in the background. It's a simple fact that the more a product is used, the greater the possibility of resistance evolving, so it's good practice not to use sprays unless they are actually needed (and actually effective for the problem at hand, but that's another conversation), certainly in the home garden where a failure of one crop is not going to cause destitution.
c) spraying pre-emptively makes me think of ads for Rogaine and other baldness prevention treatments, the sort that have to be used before there's any sign of hairloss - all that money spent and you'll never know whether it was actually necessary or not!

On the bug front one thing that may help you in the long term is to stop thinking about 'bugs' as one amorphous group, and not to assume that they all must die. Control of earwigs is vastly different to control of caterpillars, for example. Also, it helps to think about what part of the crop is being attacked, and whether action is really needed. Fruiting crops can take leaf damage in their stride once they get a bit of size, whereas leaf damage on leaf crops is clearly worth acting on.

Good luck with your gardening! Pest control can actually be an interesting part of gardening, if you look at it as a challenge in outwitting the pest/disease. It's also a great opportunity to extend your knowledge of the biology and behaviour specific pest species, and the way they interact with their host plants and their predators.