Use sand to mark out the design of the whole bed before you start planting. Work from the center outwards or from the back of the bed to the front. Use a plank, a kneeler or a piece of wood for kneeling on so that the soil does not become compacted. If compacted, it will become difficult to work and will inhibit the drainage.
After you have finished marking out the design, place the plants, still in their containers, roughly in position on top of the prepared soil to ensure that the bed will be neither too crowded nor too sparsely planted. Consider planting groups of 3, 5 or 7 plants of the same type for a more compact look or if you are planting a more complicated design, with shapes and patterns, place the plants evenly into the marked area. Make any final adjustments to plants positioning because it will be too late to do it once the plants are in the ground. Keep a few plants in reserve to replace any that may die after planting to avoid gasps into your final design.
Plant the seedlings carefully, handling the plants as little as possible. Firm the soil around each plant while planting each of them. Complete one section of planting before moving on to the next section. As each section is completed, trim off any damaged, uneven or straggly shoots to make the patches of plants more compact. Water thoroughly section by section so that seedlings that were planted first do not dry out while the others are being planted.
Continue planting each section until you have finished the whole bed or border. Water regularly and weed if necessary. Replace any plants that did not survived through the process with the plants from your reserve. This way the bed will look healthy and compact.