If you don't have much garden experience, I'd recommend getting a landscape plan from a landscape architect. Plans tend to be relatively inexpensive; it's hiring people to implement them that costs.... A landscape architect should look at the whole space, not just a specific patch, and help everything flow together. Which is not to say you have to landscape your whole yard. The plan would look at the area in relation to the house and yard, not just the porch, so all the elements around your porch could be better balanced.
As far as plants go, perhaps you should start by thinking about what overall effect you want. Are there colors or textures you particularly like or dislike? For example, I find I like a "fluffy" quality to plants, a kind of visual fullness, so I like things like coreopsis and Russian sage, but some people like strong, spiky vertical lines or neatly rounded mounds. Do you want a manicured look or something less constrained? Do you want to focus on a few terrific plants or do you enjoy the blend and contrast of different plants mixed together?