Not all perennials have the same soil requirements. For example, peonies have different requirements than ferns; native plants have different requirements than exotics. A soil test is helpful to understand overall fertility and trace mineral content but how you want to respond is dependent on the nature of what types of perennials you want to plant as well as the microclimate (sun/shade, moist/dry.)

There is a local lab that will do an analysis of your site and will provide directions for how to take samples http://www.al-labs-west.com/  i'm a big fan of perennials and I treat the name broadly in that I don't limit it to herbaceous perennials, I also include woody plants.  A mixed perennial border can provide year-round interest with different heights, textures and colors.

I'm assuming you have already done any hardscaping (patios, decks, walkways, fences, retaining walls, etc.) that you plan to do and you already have some planting areas defined.  However, hardscapes and existing foundation plantings can be elements of the overall design.

I found this handy link from Illinois extension http://web.extension.illinois.edu/gardendesign/introduction.cfm. In glancing at it, I was pleased to see it said 'look around'. I also found this one from Colorado http://www.ext.colostate.edu/mg/gardennotes/413.pdf One thing you can do is walk around your neighborhood and take pictures. If you see someone working in their yard and there are plants you like, you can usually ask "Could you tell me what that is?" and take pictures. You can also leverage people at independent nurseries. We have so many of them (some are specialty) but by asking if they can help you (set a budget!)  There are usually several people on staff that are more than happy to help you with your projects.

Most of these retail outlets have workshops and it's worthwhile to check their websites or call and see what resources they have.  Keep in mind that your garden is always changing.  If you find something that isn't doing well, look at it as an opportunity to find something that will work.