To develop your green thumb, take up gardening to feed your soul. Not to decorate your house or impress your neighbors. Study the needs of particular plants, you can get a certain amount of information from books, but often trial and error makes the best teacher. Plant catalogs, for example, tell "zones" (based on coldest annual temperature) and which plants will grow in which zones, but they fail to give other critical requirements. Like humidity, length of growing season, type of soil, and amount of shade in your yard. Ask questions and be alert, .look around your neighborhood to see what does well. For example, I would dearly love to grow a bougainvillea, I see their spectacular magenta foliage less than 150 miles from my horne. Six thousand feet down the mountain! Instead I plant honeysuckle, which doesn't mind the altitude in my yard. Be attentive, watch each plant to see if it's happy where you've placed it. Above all, be patient with yourself. Developing a green thumb is a learning process.