Easy:

Start guiminer
Got to file-> new cgminer
host: coinotron.com
port: 3334
username: yourusername.workername
password: workerpassword
device: pick the gpu
threads: 21712
worksize: 256
vectors: 1
intensity: 20
gpu threads: 1
use stratum: yes

using gpu tweak or msi afterburner:
core clock: 1100
mem clock: 1375
power target: anywhere from +10 to +20
play with mV voltage to bring it down if you want to draw less power

you should be getting about 560 kHs plus

and make sure you are using gui miner scrypt