Usually people ask for advice on how to play OS (offensive style). In fact there's *far more* discussion about DS (defensive style) in VFdc. But if you really need a quick-and-dirty guideline to get you started on DS, this is my advice:
UP CLOSE
If you are at disadvantage (usually meaning your opponent just blocked your previous move) —> choose between db+p; df+p or block.
If you have the advantage (usually meaning you blocked your opponent's attack) —> choose between p, f+k or throw.
FROM A DISTANCE
Alternate between df+k; f,f+k or B (backwalk).
If you are new to the game don't try her other deflecting (sabaki) moves for now - they require intricate guesswork that you might find difficult to grasp. Instead try randomly throwing out some low punches, f+p strings and the good old tornado kick (k+g) once in a while to keep your opponents honest and you're set, insta-DS!