This is a sad fact of the activity, especially as you start out. You are dealing with living things, and you must be respectful of that. Commit yourself to understanding why every tree dies and what can be done to prevent it. Learn from your mistakes and do your best to prevent them in the future. Try to limit yourself at first to a few kinds of plants.
Every tree is different.
Likewise, every kind of tree is different. Learn to care for a few different types of plants, and grow your collection from there as you expand your design styles. It is impossible to write a simple set of care rules. Every species of plant has it's own special needs. Each location and environment is different too, and have to be considered.