What I have learned so far:
1. This is a lot of work! So make it count for double the time & money: add nutrients while you mulch.
2. Apply it 2-3 inches deep to suppress weeds for the growing season. You still may get some, but usually they are easier to pull out of the loose mulch than the firm soil.
3. Make sure to leave your plants some wiggle room. Apply the mulch deeply, but leave it at least one inch away from the crown of the plant. Leave 2-3 inches of space all around tree trunks.