u can leave the cement floor if you have 'dispersers' on the ceiling,i.e. sound absorbing materials,so you don't get that nasty bouncing 30-50 milisecond delay(floor-ceiling-floor and so on),but people usually don't wanna bother with working on the ceiling, 'cause it's much easier to put some carpet on the floor,and few of the absorbing materials on the ceiling...
-helps if you put panels around the drums,so the sound is more 'direct'(and absorber directly above the drum but only IF the drum itself is way too present in the mid/high area(snare,cymbals)
-bass traps in corners(never go for square shaped rooms)
-try to move the 'control table' around the room untill you find the sweet spot,then put some absorbers on the wall in front of it,and behind(though,it IS much better to 'coat' the whole damn room..i always went for 'room inside of a room'-where the hollow points between the cement wall and built wall are filled with sound and heat/water resistant materials-though this is a bit expencive,and takes time)
-put the drums lil' bit higher off the ground (20-30 cm),this way the kick will be more present
....think that covers it....
i've owned/worked in several studios,and this was always the fastest way to get to a good startin' point....bass traps and sound absorbers are the most crucial,if you want to get a normal sound for rehersal...