1. Pick the Perfect Container
The container is just as important as the plants. It ties the whole composition together, acts as a functional piece of decor and sets the tone for the style you wish to convey. I like to choose the pot first because while there are plants in all sorts of colors from which to choose, I have a harder time finding decent containers at reasonable prices.
If you choose a brightly colored pot it can make a dramatic statement, but only if the plants are bold enough to hold their own. The plants don't have to have bright colors, mind you. The sleek and modern simplicity of a cast iron plant (Aspidistra) or snake plant (Sansevieria) would be just as dramatic.
2. Select a Plant to Complement the Container
Now choose one plant that shares something in common with the container, be it color, texture, pattern or shape. For example, I used the bright yellow splotched leaves of a 'Florida Beauty' Dracaena to tie in with the bright pot.
3. Select a Plant to Contrast with the Container
First of all, bear in mind that these plants will be growing together, so they will need to thrive in the same conditions. A contrasting plant is simply a plant that is in some way the opposite of the first plant. If the first plant has dark leaves, choose a plant with light green or silver leaves. If the first plant is light pink, combine it with deep green. I chose a Vriesea sucrei hybrid as my contrasting plant for the deep reddish purple undersides of its leaves, which are opposite on the color wheel from chartreuse. Here's a color wheel to assist with your design. For a handy sliding color wheel, you can buy a real one from Dick Blick for a song!
4. Select a Plant to Tie Them Together
When you end up with two plants that are total opposites on the color wheel, the result can be a bit garish. To soften the effect, choose a third plant as a buffer. It could either share some characteristics of both plants, or it could be a mixture of both colors.
In the case of my chartreuse Dracaena and purple bromeliad combo, I chose Satin pothos (Scindapsus pictus). The leaves are of a similar shape to those of the Dracaena, they meet halfway between the contrasting plants with their dark muted green color and they also share a similarly splotchy pattern.
5. Arrange the Plants
To really make the bold colors work, a little thoughtful arranging goes a long way. Try to plant in varying heights so that the composition has a natural flow. The classic arrangement of 'thrillers, fillers and spillers' includes an upright dramatic plant to act as the 'thriller', a bushy mid-height plant as the 'filler' and a trailing plant such as a vine as the 'spiller'.
Usually the tall 'thriller plant is in the middle of the arrangement, but when it comes to houseplants I like to deviate a bit by placing the tallest plant in the back. While the natural lighting outdoors might be more or less even from all sides, interiors are usually lit from the side by windows, which causes plants opposite of the window to die out. With the plants arranged in a stairstep fashion, they can efficiently use the available light and keep their full appearance.
To accomplish the stairstep effect, it helps to know in which direction the plant will grow. The 'Florida Beauty' Dracaena will grow upwards in time, but to give it a little instant height I used a stick to act as a stake. Skewers and chopsticks work well too.