My first suggestion (and I always bring this up at garden clubs), is decide where your pot is going to be placed before planting. It will be heavy. however, you don't have to fill the whole pot up with potting soil, just make sure you have a good drainage hole. I always put a piece of landscape cloth over the hole to prevents slugs, etc., from crawling up. Coffee filters rot away too quickly. Then, if it's a very large pot I put some empty plastic soda or water bottles in the bottom to displace some of the soil (leave the caps on). The plant usually doesn't require a huge pot full of soil. I don't use packing peanuts -- too messy if you need to repot, and some of the newer packing ones are now water soluble.
Then you can have some fun picking plants. I always like the "thriller, filler, spiller" effect. A taller plant in the center, with about three other kinds (same variety) around this and then a couple of plants that spill (hang over the sides of the pot). I like Cordelyne as the taller plant. I've used Pentas, Salvias, Snapdragons, Petunias and other annuals just for the color. Creeping Jenny makes a lovely spiller. You could also think of a dwarf fruit tree.
