There are two things to consider in fllower garden design. Especially when you consider yourself a beginner. One is the location and the other is you. Let’s look at location first.
What do you have to work with? Sketch out your yard on a plain piece of paper and then on a sunny day, mark the areas that have full sun, partial sun, full shade, and any other variations that you can find. You may need a couple of copies of this paper before you begin because morning sun is different from afternoon sun. Mark the directions on the paper too. Now you can see where the full eastern sun hits and the full western sun.
I made a big mistake with my geraniums the first year by putting them where they could be seen from the street. Unfortunately that was at the northeast side of the house and the geraniums spent half their day in the shade of the house. They did not like this very much. They bloomed but they were not hanging with blooms like they should have been. So take note of the sunlight and match your garden choices with the sunlight available.
Your sketches will guide you to the bed locations that would be best to begin with. Likely you will have several options. You want them to be in a highly visible place and your first choice should be a location that is highly visible to you. Where do like to sit in your home? The living room? At the kitchen table? Sit in that spot and look at the choices on your piece of paper. Which one is most visible from where you sit?
That is the place to begin.
Okay. Now step two of the design is to actually layout the bed. This is where you have to do a serious self assessment. Are you the type of person who takes on way too much work and then gets overwhelmed? Go for perennials. Are you the obsessive type who likes to keep rearranging things? Go for annuals. Do you have a lot of time? Start with two beds and experiment with different layouts for your flowers.
What? You don’t know what kind of person you are? Here’s a quick way to figure yourself out. Pick up some of those gardening magazines you have around the house. (Yes, I know you have them.) Now flip through the pages and mark each page that has flowers that appeal to you.