Listed below are some commonly used crochet abbreviations:

alt alternately
approx approximately
beg beginning
CC contrasting color
ch chain(s)
ch sp chain space
cl cluster(s)
cont continue
dc double crochet
dec decrease
dtr double triple crochet
ea each
est established
fol follow(ing)
grp group(s)
hdc half double crochet
hk hook
inc increase
LH left hand
MC main color
No. number
oz ounces
pat pattern
prev previous
rem remaining
rep repeat
RH right hand
rnd round(s)
RS right side
sc single crochet
sk skip
sl slip
sl st slip stitch
sp space(s)
st stitch(es)
tog together
tr triple (or treble) crochet
WS wrong side
yd yard(s)
yo yarn over