A figure 8 is sufficient, especially if you trace it through like a water or tape knot - with the tail ends going in opposite directions through the knot, if that makes sense. The best knot I like for a pair of loops you're gonna use for a long while is the double fisherman's knot. Describing things in words is tough, but basically lay your cord in front of you, with the ends lapped past each other with enough extra to tie the knot. Take one end and tie an overhand around the other tail, passing the end through the overhand loop an extra time. Cinch it onto the line and slide it over to make room for the other half of the knot. You now take the other tail end and do the same thing on the other side. Once you dress the knot it will take an act of Congress to untie. The advantage is that the part of the knot bearing your weight only goes through gradual bends, not a total reverse as in most other knots. Sharp bends in knots constitute the weak points, or failure points, in your rig. These really become important in the event of a fall.
A great inexpensive primer on knots for climbing is John Long, Ropes, Knots and Slings for Climbers. If you want the full details of modern American SRT, get On Rope by Bruce Smith & Alan Padgett.