Answer: In some ways gardening is as much trial and error as science, so it's no wonder there is so much conflicting information. You will also come to discover that gardening is regional in many respects so that instructions written for say England or Oregon may not be suitable for your area. You will learn a lot by trial and error in no time!
Soil preparation can be done anytime, and fall is ideal because it allows the soil to settle prior to planting the following spring. Winter can also help weather clay soil and improve its texture a bit. Your first step would be to run some basic soil tests to see what amendments are (and aren't) needed and work from there. Clay soil always benefits from the addition of copious amounts of organic matter -- chopped leaves, compost, aged stable manure and bedding, and so on are all good sources. Your County Extension should be able to help you with the tests and interpreting the results.
Spring blooming bulbs are planted in the fall. They generally require excellent drainage so in a heavy soil they may need a raised bed or do better on a slight slope. Bulbs make a wonderful spring display but must be left in place after they bloom so that the foliage can replenish the bulbs and then eventually, cure and dry. This can be ugly unless you can hide them inbetween or behind perennials or other plants. It is a choice you'll have to make.
Two books I would suggest as being straightforward and genuinely helpful are "Gardening for Dummies" by Michael MacCaskey (ISBN 1-56884-644-4) and "Perennials for Dummies" by Marcia Tatroe (ISBN 0-7645-5030-6). These both include information about site evaluation, soil preparation, plant selection and ongoing maintenance as well as sample plans. Another book I particularly like is "Rodale's Illustrated Encyclopedia of Perennials" by Ellen Phillips and C. Colston Burrell (ISBN 0-87596-570-9).
Enjoy your garden!
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