How can I work out my biceps?

ive been woking my biceps for 8 or 7 months , ive noticed considerable growth , but i think my biceps are becoming slim again , when my biceps where bigger i lifted 10kg , and made 300 repetitions (30 x 5 , then 25 x 4 , and finally 20 x 5 ) but now i lift 14 kg (30pounds i believe ) and I work out : (25,25, 20,15,15, and 10 ,10,10,10,10,10,10,10,10,10) , am I working out correctly or what can I do to enlarge my bicep ?