There's really no way to incorporate an above-ground propane tank into an attractive landscaping scheme. They're inherently ugly items, but they are necessary to the home, so finding ways to camouflage, hide and de-emphasize them will be the key to successful landscaping around them. Rather than planting beds of bright flowers at the base of the tank, which only draws the eye, use screens, shrubs and good design principles to work around the propane tank.
Put up a decorative screen, fence or trellis around the tank, perhaps with a gate for easy maintenance access. This still looks like a structure in your yard, but at least you can choose a color, style or material that suits the rest of your landscaping and complements your home. Be sure any fencing is at least 2 feet away from the tank.
Encourage vining plants to grow on the trellis or screen you've chosen to hide the tank. Good examples are climbing roses, morning glories, ivy, honeysuckle, jasmine or even beans or peas if you prefer growing vegetables in that space.
Use shrubs as a privacy screen or landscaping element that shields the tank from neighbors, passersby or the windows of the house. Plant them strategically to screen undesirable views, and choose evergreen shrubs for year-round service. Juniper, holly, photinia or nandina are good year-round choices that also provide color and interest in the landscape. Be sure to choose plants that will grow tall enough to hide the tank, usually about 6 feet.
Consider planting ornamental trees. If you plant young seedlings in a row or box surrounding the tank, you will have a pleasant view from all sides when the trees are grown. Fruit trees like apple, cherry or pear are often both decorative and productive in the home landscape, for example. Be sure to plant trees at least 10 feet away from the propane tank so their roots don't extend to interfere with the tank.
Resist the temptation to paint your propane tank a more pleasing color. Dark colors or matte paints that are not manufacturer-approved can cause the tank to retain more heat than is wise; increased heat can cause the tank pressure to go up and the safety relief valve to open unexpectedly.