Set up your own gear, turntables, mixer etc. just as you would at home. Use a pair of headphones to check that everything is functional, check the levels are normal, and nothing sounds drastically different to how it did at home. Many of the controls on your mixer will be set at a standard level, and you will rarely, if ever, have cause to adjust them. But a trip to a venue in the back of your car or in a backpack can shift them around quite dramatically.
Be sure that before you connect anything to the PA mixer, all levels are set to zero.
Connect the master output of your mixer to one of the input channels on the PA mixer using the appropriate cable. Most professional mixers use an XLR connector, like you would find on a microphone, for the high output and good signal to noise ratio. It's a good idea to check in advance that you have compatible equipment with your venue, as it's not ideal to find out right before a set that you can't connect to the sound system.
Play a few of the songs from your set, ideally before any of the audience arrives. This will allow you to check again that no controls have moved in transit. Use the equalizers on the main desk to tune the bass, middle and treble to suitable levels. Remember that once you're on stage, you won't be able to adjust these any further, so avoid using any extreme settings that might sound great on your first song, but terrible on the rest of the set.
Secure loose cables and tape down any that run along the floor. Once the room is full of people, it is surprising how easily the only loose cable in the room can be tripped over, causing a sudden, unwelcome silence during your set.