
A spot in the the sun or with only partial shade, a nice flat location without the interference of tree roots or branches. You don't want to place your garden in a spot where the dog or the mailman will cut through and you want a place that has access to a hose or water source.
There are a couple of considerations here. First, you don't want to bite off more than you can chew and you want an area that you can reach from one side to the center. A rule of thumb is that your garden should be a foot or so longer than you are tall and no more than 3-4 ' wide.
In the beginning you will need a good pair of gardening gloves, some trash bags, a bag or two of manure, several bags of compost and a shovel with a bit of a point.
Mark off your rectangle. Rectangles are for beginners - hold on to your curvy design ideas until you have more experience under your belt. Once you have marked off the spot you can begin clearing. You need the spot to be free of all grass, weeds, and trash. Then dig down about the depth of your shovel and turn and flip the soil over and over. Once the area is clear spread the manure and compost. Try and get the area as level as possible. After the area is level, give it a nice gentle shower with the hose.
The most important thing for a beginner is that you choose the right flowers for the amount of sunlight your bed receives. Flowers come with labels that will tell you exactly what they want. Beyond that choose the flowers that you like but give some thought to having flowers of differing heights so that your bed will have dimension.
Dig a hole for each plant. You'll know the hole is deep enough if the container that the plant is in fits into the hole. Turn the plant upside down and gently pull the plant loose from the container. The plant should slide out easily. If the plant doesn't come out tap the bottom of the container. Do NOT pull on the leaves or any other part of the plant. \015\012Put your plant just deep enough into the ground so that it's set at the same depth as it was in the pot.
You'll need to spread some mulch very gently on the bed being careful not to get it on the plant or too close to the base of the plant. You should water the bed immediately after planting and then every four or five days thereafter. Watering takes patience. Too much water pressure because the hose is on the wrong setting can do damage to your plants. Chose a gentle shower setting and enjoy the calming back and forth motion as you water your new masterpiece.