My thumb is getting darker. How do you garden without killing everything?

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Help! My green thumb has turned black! Four years ago my dh & I installed these great beds along the front of our house. We put in a couple dwarf trees, a green laceleaf maple, about 100 tulip bulbs, 2 hyacinths, and some roses. Last summer I added some daylilies to the mix. And of course a selection of annuals. I read the books on soil acidity, sun & water requirements, etc, yet somehow only 2 daylilies and the 2 dwarf trees are still standing. The maple didn't bud this year. The hyacinths look like they're being attacked by some sort of critter (japanese beetles, maybe?), and only 5 tulips came up in the spring. Even the marigolds died this summer. So what are some good, sturdy plants that even a horrible gardener like me can keep alive (preferably with blooms, not just green)? And what do I have to do differently to keep them alive? I live in an area with warm summers (~90 F) and cold winters (lots of snow). Thanks!