The traditional method is to dig a trench and place the seed potato inside and cover it. Then as the potatoes grow, soil is mounded over them.
I have used this method with good results, but the problem is that it is very labor intense (all that digging) and harvesting is a pain because I end up spearing many potatoes with my garden fork and end up not finding them all.
So this year I am trying something new.
The first was the Straw Method:
1) Take your loose soil bed (Top with some compost)
2) Place (or throw) a potato on top of the soil about a foot apart for each other(no digging..yah!!)
3) Cover with soil
4) Cover with a little straw
5) When they grow to about 6-8inch, mound up with more straw
6) Repeat step five until you have a large mold of straw around your potato plant
7) Stopped mounding when the plant flowers
The idea with this method is that the potatoes will grow outward in the loose straw providing a huge crop with ease of harvest (just uncover the straw)
Potato Bag Method
1) Put some compost about 4-6 inch at the bottom of a potato bag. I bought special potato bags, but I think one of those nylon grocery bags would do fine with a few holes cut for drainage in the bottom.
2) Place 3 small seed potatoes in the bag away from each other.
3) Cover with straw once they get 4-6 inches
4) Cover with potting soil when the grow another 4-6 inches for the second mounding
5) Cover with straw then soil until the grow over the top of the bag
Note: You can use other containers like plastic storage tubs, large pots, or wooden crates. Some people use car tires and stack them, but I do not recommend this because I feel tires can be toxic.
With both methods, harvest once the plant dies back.