So if you know my husband, we couldn't just put the rain barrels on the ground and be done with it. We cleared out the area where they were to go and covered it with landscaping fabric. Then we built a "platform" for each barrel using concrete pavers. In our case it all had to be level :) We elevated one barrel so that once it's full it will spill over to the next barrel.
Next we covered the landscape fabric with egg rock. The first barrel is attached to the down spout on the house. We purchased a hose online that connects the two barrels. We also purchased a diverter that connects to the downspout and the first barrel. It senses when the barrels are full and diverts the water into the yard. Pretty cool and saves a tremendous amount on the water bill. Now all we need is for it to rain!