The most basic and critical information here is simply: Green side goes up. Start with that, and you'll be well on your way to happy gardening.
Planting depth: When transplanting out of a container, put plants in the ground at the same depth they were in their pot. Too deep planting is lethal, particularly for most trees and shrubs. Too shallow planting will lead to roots drying out. Bare root plants and bulbs can be harder to judge. In general, bare root perennials will have a clear crown – a point at the top where all the roots are coming from, and usually some fat buds are waiting to grow into new stems and leaves. That crown should be at or just slightly below the soil surface. For bulbs, the rule of thumb to plant at a depth 2-3 times the thickness of the bulb is generally a good one, but most plants are not very picky. Very deeply planted bulbs will be slower to emerge and better insulated from winter cold, while shallowly planted ones will be more likely to dry out and suffer from drought. Almost all bulbs, however, will move themselves in the soil after just a year or two to the position they like best, so starting position is usually more or less irrelevant in the long term.
Planting time: I put plants in the ground pretty much any time from spring through early fall, provided we're not in the middle of a heat wave. Early spring plantings are nice because the cool weather and ample moisture gives plants plenty of time to establish before the heat and dry of summer. In our climate, summer plantings are usually fine as well, provided you are very careful to keep up on the watering while they get established. Fall is actually one of my favorite times to plant because it isn't nearly as busy as spring and the weather is often perfect for letting transplants settle in. The one exception is when you are planting something that you aren't sure is going to be hardy. For those, always plant in spring so they'll have the longest period possible to settle in and get established before they have to face the winter that may well kill them.
Local climate: The key to growing happy plants is getting them in the right spot. This starts with understanding your local climate. The information in our catalog is based on growing plants here in zone 5 Michigan where we have cold, snowy winters, warm but rarely extremely hot summers, and usually consistent, plentiful summer rain fall. The more different your local climate is from what we have here, the less useful our experience with any given plant will be. To be successful, get local advice, and then experiment, noting what plants do best in your conditions. A plant that loves your climate will grow well even if you make a lot of mistakes. One that is already stressed out by too much heat or cold leave you very little room for error.
Sun versus shade: This difference is less critical than most novice gardeners believe. Too much or too little sun will rarely kill a plant out-right. Too much sun is more lethal, causing leaf burn and increased sensitivity to drought, while too much shade generally results in slow growth, reduced flowering, and a long, slow, lingering decline. If you aren't happy with how a plant is performing, experimenting with more or less light may solve the problem.
Soil and drainage: This is very critical. Heavy, wet, clay soils are the kiss of death to alpines and other plants that like good drainage. Light sandy soils are more forgiving, but drought is a bigger problem. Raised beds are an easy way to provide good drainage over clay soil, and adding lots of organic matter and thick mulch will increase the water holding capacity of light sandy soils. Understanding what grows well in your soil conditions and embracing those plants will make your life as a gardener a lot easier than trying to fight it to grow something that just isn't suitable.
Watering: We don't water plants in the ground here at Arrowhead. Every new planting gets watered thoroughly when it is first planted to settle it in, and maybe during the first year in the ground if there is a particularly hot dry spell, but after that, in our climate, irrigation simply is not required, even on our very light, sandy soil. This may or may not be true in your climate, but in general, gardeners water far more than they need to. Perversely, frequent watering also makes plants less tolerant of subsequent droughts. Treated to regular water, they grow fat and lush with shallow root systems, and then when drought comes, they shrivel up and die. Un-irrigated plants, on the other hand, will grow smaller and tougher with deeper roots and sail through drought unharmed. So, if you must water in your climate, the rule is to start watering as late as possible to build up the toughest plants, and then once you start, keep it up regularly until the drought breaks.