Our preferred method was to give people twelve goes at rolling 3d6, assigning the attempts before you saw the roll. You had to giive each characteristic at least one 3d6 roll, but the rest could be assigned as you wanted. So if you were determined to roll a Fighter with high Strength and Constitution, you could put one 3d6 roll into the other four stats and have four rolls at each of Str and Con, putting the best one in. You occasionally got low results on stats you really wanted to be high but it wasn't common, and sometimes the other stats would surprise you.