When your potatoes arrive, store them in a cool, light place (the refrigerator will not do) if you are not ready to plant them. The best planting time is two weeks before last frost; if planted too early, the shoots can be damaged by freezing temperatures (although they will usually regrow). Give them a soil that is deeply dug and moderately fertile, to which compost, neither manure nor lime have been added within the last year. Clay soil should be lightened by adding compost and or peat moss.
The "mini-tubers" you have received will produce excellent yields when planted whole. Plant in rows 30 inches apart at a distance of 12 inches apart in the row, 2 to 4 inches deep. Hill them with soil as they grow, to keep the ones near the surface from "greening". The easiest way to do this is to plant in a shallow trench, then hoe soil around them from time to time as the plants grow taller.
Potatoes grow best in a soil that remains cool and evenly moist. A mulch of hay or straw is the best way to achieve this, and will also help the plants to resist pests. As soon as the shoots break ground, place the mulch next to the potato row, leaving just enough space to let in some light for growth, then add more mulch if needed as the plants grow. Avoid mulch if voles are a serious problem in your garden, since it provides a hiding and nesting spot.
Start harvesting baby new potatoes as soon as you can snatch a few from the edge of the hill. Continue to dig them until hard frost, and then store any that remain.