Soil is the most important thing in your garden. It is where all the action is. The better your soil - the more micro-organisms moving around, along with nutrients and water.
Soil is basically three types - sandy, loam or clay. A great way to test your type is to pack some into a baseball shape in your hand. If you poke it and it falls totally apart - your soil could be too sandy. If it mostly keeps its shape it is loam - which is the consistency you want. If you can't poke your finger in at all it has too much clay. If you are building a new garden and removing sod, you will need to amend to get the soil party started. A triple mix soil blend is beneficial when as the peat moss will help retain moisture, the topsoil will help change the consistency of your most likely compacted and nitrogen deficient soil, and the compost will add organic matter to help those microbes get moving.
Water is what is going to bring your plant roots all the goodness from the soil. Smaller plants you have to water more often. As plants get larger, space out the waterings more, but ensure that the soil is saturated deeply. When you water too little too often - your roots grow horizontally as that is where the water is. When you water less often but for longer, the roots learn to grow down instead of out. This proves extremely beneficial in dry Stretches where deeper rooted vegetables will have better access to water to keep producing lots of vegetables, as well as for anchoring the plant when heavily laden with big fat veggies and strong winds. Generally, yellow leaves indicate over watering, and brown show under watering. Only water in early morning or late at night.
Transplants from inside your house should be hardened off for a couple of weeks prior to garden planting. Put them in an area protected from the wind and any pets, and out of any strong direct sunlight. Stay on top of watering. Make sure your seedlings have been watered well to help with the transplant shock, they will likely wilt after transplanting - fear not - they will bounce back. Keep the soil wet. As much as possible, do not directly disturb root systems when transplanting, take a wide rootball. When direct seeding, water soil the night before.
Pests and Disease.
The number one thing you can do to help minimize your chances of pests and disease is to keep your garden tidy. the more piles of weeds in your garden, or plants that have snapped stems and are lying on the ground - the more problems you will have. Both bugs and disease often love moist environments, don't give them any. The next thing is to act fast. The first sign of trouble you need to identify what it is you are dealing with - Google images is great for this. Bird feeders, sunflowers and bee attracting plants are all great organic measures to bring beneficial birds and bugs into the garden to help alleviate those harmful ones.