Just go to
https://bitcoinfees.21.co/ and enter the recommended fee per byte (70 satoshi at the time of this post) and multiply it by 1000, then enter that amount in Tools > Preference > Transaction fee per KB. But I've been using 0.0005 per KB
byte for most transactions and they always get through very fast.
Enter the amount based on your base unit though. Some people have sent 0.0005mBTC by accident when it should be 0.0005BTC.
Edit:
Mistake (noticed 2 days later). I meant 0.0005 per KB and not byte. I'm not that rich.